diff --git a/.changeset/quick-hawks-bark.md b/.changeset/quick-hawks-bark.md
new file mode 100644
index 000000000..ec7a8af7f
--- /dev/null
+++ b/.changeset/quick-hawks-bark.md
@@ -0,0 +1,5 @@
+---
+type: Added
+pr: 2422
+---
+**`<precondition>` task element (Design by Contract)** — plans may now declare a runnable/checkable fact a task assumes (env var set, prior-phase artifact present, external-setup done) that plan ordering does not guarantee; the executor asserts it before running the task and halts with a checkpoint on unmet instead of building on a broken assumption. Plans that omit `<precondition>` behave exactly as today. (#1949)
diff --git a/CONTEXT.md b/CONTEXT.md
index 7b1dd2500..9933d3381 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -362,7 +362,10 @@ Phase 1 deliverable under `--mvp` on a new project — the Phase-1 whole-applica
 Single-feature task that moves one user capability from open-to-close (happy path) end-to-end. Contrast with the horizontal layer (all models, then all APIs, then all UI). The default planning unit under tracer-first decomposition (the leading task is a Tracer Bullet); SPIDR Splitting axes (Spike, Paths, Interfaces, Data, Rules) are the canonical decomposition tools when a slice is too large for one phase.
 
 ### Tracer Bullet
-The default GSD decomposition lead: a **permanent, production-quality, minimal end-to-end slice** that wires one path through every layer a phase touches and becomes part of the skeleton of the final system — written for keeps, not thrown away. Contrast with a **prototype** (throwaway reconnaissance code, deleted once its lesson is learned): a tracer's *functionality* gaps are acceptable but its *architectural* gaps are not; stubs are allowed only where they can later be filled without an architectural change. GSD ships tracers, never prototypes — which is why `gsd-planner` LEADS every plan with a `type="tracer"` task (default; `--no-tracer` / `TRACER_MODE=false` opts back into horizontal layers) and `gsd-executor` runs an early integration feedback gate on the tracer's `<verify>` before expansion tasks (autonomous: halt-on-fail; interactive: `checkpoint:human-verify`). Origin: *The Pragmatic Programmer* "Tracer Bullets" (#1945); the Walking Skeleton is the Phase-1 whole-application special case. See Vertical Slice, MVP Mode, Walking Skeleton.
+The default GSD decomposition lead: a **permanent, production-quality, minimal end-to-end slice** that wires one path through every layer a phase touches and becomes part of the skeleton of the final system — written for keeps, not thrown away. Contrast with a **prototype** (throwaway reconnaissance code, deleted once its lesson is learned): a tracer's *functionality* gaps are acceptable but its *architectural* gaps are not; stubs are allowed only where they can later be filled without an architectural change. GSD ships tracers, never prototypes — which is why `gsd-planner` LEADS every plan with a `type="tracer"` task (default; `--no-tracer` / `TRACER_MODE=false` opts back into horizontal layers) and `gsd-executor` runs an early integration feedback gate on the tracer's `<verify>` before expansion tasks (autonomous: halt-on-fail; interactive: `checkpoint:human-verify`). Origin: *The Pragmatic Programmer* "Tracer Bullets" (#1945); the Walking Skeleton is the Phase-1 whole-application special case. See Vertical Slice, MVP Mode, Walking Skeleton, Precondition.
+
+### Precondition
+The front-of-task side of the GSD plan contract (issue #1949, *The Pragmatic Programmer* Topic 23 — Design by Contract). An optional `<precondition>` element on `<task>` stating, in a single line of runnable/checkable prose, what must already be true for the task to begin safely — e.g. "`OPENAI_API_KEY` is set", "`dist/schema.json` from Phase 02 exists", "server responds to GET /health". `gsd-executor` evaluates it before any other task work, using **read-only checks only** (file existence, env var presence with no value output, idempotent `GET /health`-style pings — no writes, no network POSTs, no secret emission; if a side-effecting check seems required, the executor halts and surfaces a checkpoint rather than running it): met-or-absent is a no-op (back-compat for every existing plan); unmet returns a `checkpoint:human-verify` with no partial commit, and is NEVER auto-approved under `AUTO_CFG=true` (a missing prerequisite is a fact the executor cannot establish on its own, not a verification step). `gsd-planner` emits `<precondition>` in exactly three cases — `user_setup` consumption, prior-phase artifact dependency, or env-var/runtime-config dependency — when the assumption is not already guaranteed by `depends_on` ordering. Closes the contract triad whose other two sides are postconditions (`<verify>`/`<done>`/`<acceptance_criteria>`) and invariants (`must_haves.truths`). The structural validator (`cmdVerifyPlanStructure`) does not reject unknown optional tags, so adding `<precondition>` passes plan-structure validation unchanged. Canonical schema reference: `docs/reference/plan-md.md` → Preconditions; emission rules + anti-patterns: `gsd-core/references/planner-preconditions.md`. The architectural-end companion is the Tracer Bullet (#1945); together they close both ends of the "outrunning your headlights" failure mode. See Tracer Bullet.
 
 ### Behavior-Adding Task
 Predicate over a PLAN.md task: `tdd="true"` frontmatter AND `<behavior>` block names a user-visible outcome AND `<files>` includes at least one non-`*.md` / non-`*.json` / non-`*.test.*` source file. Pure doc/config/test-only tasks are exempt. The MVP+TDD Gate (in `references/execute-mvp-tdd.md`) only halts execution on this predicate; the gsd-executor agent applies all three checks at runtime. Currently a prose-only specification — no shared utility.
diff --git a/agents/gsd-executor.md b/agents/gsd-executor.md
index 3e2db5fe2..78cac9406 100644
--- a/agents/gsd-executor.md
+++ b/agents/gsd-executor.md
@@ -144,6 +144,10 @@ At execution decision points, apply structured reasoning:
 
 For each task:
 
+0. **Precondition check (before any other task work):** If the task carries a `<precondition>` element, evaluate that single prose line first — it names a runnable/checkable fact the task assumes (env var set, prior-phase artifact present, server responding to `/health`, `user_setup` step done). Verify with **read-only checks only** — file existence, env var presence (no value output), idempotent `GET /health`-style pings. Do NOT run commands with side effects (writes, network POSTs, secret emission) as the check; if a side-effecting check seems required, halt and surface via checkpoint instead.
+   - **Met OR absent:** continue with no visible change to execution flow. The precondition is a no-op for the rest of the task loop.
+   - **Unmet:** STOP — return a `checkpoint:human-verify` (use `checkpoint_return_format`) with `**Blocked by:** Precondition not met: <precondition text>`. Do NOT partial-commit the task. Unmet preconditions are NEVER auto-approved, even under `AUTO_CFG=true` — a missing prerequisite is not a verification step a human can rubber-stamp; it is a fact the executor cannot establish on its own. The human either satisfies the precondition (sets the env var, completes the `user_setup` step, regenerates the artifact) or reruns `/gsd:plan-phase` to restructure.
+
 1. **If `type="auto"`:**
    - Check for `tdd="true"` → follow TDD execution flow
    - Execute task, apply deviation rules as needed
diff --git a/agents/gsd-planner.md b/agents/gsd-planner.md
index 50881ec67..e5b2a51ad 100644
--- a/agents/gsd-planner.md
+++ b/agents/gsd-planner.md
@@ -193,23 +193,19 @@ Every task has four required fields:
 **Grep gate hygiene:** `grep -c` counts comments, so header prose can be self-invalidating. Use `grep -v '^#' | grep -c token`. Bare `== 0` gates on unfiltered files are forbidden.
 
 <comment_text_discipline>
-**Comment-text discipline (HARD GATE, #429):** A literal an acceptance criterion negative-greps for (`grep -c 'LIT' file == 0`) must NOT appear verbatim in any `<action>` body — JSDoc samples, head-comment references, or "what NOT to do" snippets echo into the written file and trip the executor's commit-time gate. `validate_plan` (`verify.plan-structure`) fails plan creation on violation. Rephrase the literal by concept, or — when it must legitimately appear — add an allowlist marker on its own line:
-
-`<!-- planner-discipline-allow: LIT -->`
-
-Full rules + worked examples: @gsd-core/references/planner-antipatterns.md ("Comment-Text Discipline").
+**Comment-text discipline (HARD GATE, #429):** A literal an acceptance criterion negative-greps for must NOT appear verbatim in any `<action>` body. Full rules + `<!-- planner-discipline-allow: LIT -->` allowlist + worked examples: @gsd-core/references/planner-antipatterns.md ("Comment-Text Discipline").
 </comment_text_discipline>
 
 <region_scoped_negative_gate>
-**Region-scoped negative gates (WARN, #968):** Region-scope a file-wide negative grep when a sibling task needs that construct elsewhere in the same file; `validate_plan` WARNS. See: @gsd-core/references/planner-antipatterns.md ("Region-Scoped Negative Gates").
-
-**Verify-gate hygiene (#1478/#1479):** See @gsd-core/references/planner-antipatterns.md.
+**Region-scoped negative gates (WARN, #968)** and **Verify-gate hygiene (#1478/#1479):** @gsd-core/references/planner-antipatterns.md.
 </region_scoped_negative_gate>
 
 **<done>:** Acceptance criteria - measurable state of completion.
 - Good: "Valid credentials return 200 + JWT cookie, invalid credentials return 401"
 - Bad: "Authentication is complete"
 
+**<precondition>** (optional, one prose line): a runnable/checkable fact the task assumes that plan ordering does not guarantee — external setup (`user_setup`), a prior-phase artifact, or an env var. The executor asserts it before running the task and halts on unmet. Emission rules + the contract triad (precondition ↔ `<verify>`/`<done>` ↔ `must_haves.truths`): @~/.claude/gsd-core/references/planner-preconditions.md.
+
 See @~/.claude/gsd-core/references/planner-guidance.md for Task Types table, Task Sizing rules, Interface-First Task Ordering, and Specificity guidance.
 
 ## TDD Detection
diff --git a/docs/INVENTORY-MANIFEST.json b/docs/INVENTORY-MANIFEST.json
index 31a3c753b..d445161cd 100644
--- a/docs/INVENTORY-MANIFEST.json
+++ b/docs/INVENTORY-MANIFEST.json
@@ -254,6 +254,7 @@
       "planner-interface-context.md",
       "planner-load-graph-context.md",
       "planner-mvp-mode.md",
+      "planner-preconditions.md",
       "planner-reviews.md",
       "planner-revision.md",
       "planner-source-audit.md",
diff --git a/docs/INVENTORY.md b/docs/INVENTORY.md
index 8de2825bc..d6d2990cb 100644
--- a/docs/INVENTORY.md
+++ b/docs/INVENTORY.md
@@ -385,6 +385,7 @@ The `gsd-planner` agent is decomposed into a core agent plus reference modules t
 | `planner-revision.md` | Plan revision patterns for iterative refinement. |
 | `planner-source-audit.md` | Planner source-audit and authority-limit rules. |
 | `planner-mvp-mode.md` | Vertical-slice planning rules for MVP mode. |
+| `planner-preconditions.md` | Emission rules for the optional `<precondition>` task element (issue #1949, Design by Contract): when to emit, the three cases (user_setup / prior-phase artifact / env-var), format, anti-patterns, and the contract triad mapping. |
 | `planner-human-verify-mode.md` | Rules for `workflow.human_verify_mode = end-of-phase`: suppress `checkpoint:human-verify` task emission and route deferred items via `<verify><human-check>`. |
 | `planner-graphify-auto-update.md` | How `load_graph_context` surfaces `.last-build-status.json` auto-update state (running / failed / stale head) alongside the existing staleness annotation. Opt-in via `graphify.auto_update` (#3347). |
 | `planner-interface-context.md` | Interface context rules for executors — how to extract key interfaces/types/exports from existing code and document new interfaces that downstream plans will consume. |
diff --git a/docs/reference/plan-md.md b/docs/reference/plan-md.md
index 079e3a6f4..10b707d2f 100644
--- a/docs/reference/plan-md.md
+++ b/docs/reference/plan-md.md
@@ -160,7 +160,34 @@ References source files the executor needs to read. Includes project-level plann
 
 ### `<tasks>`
 
-Contains one or more `<task>` elements. Every task element must carry `<name>`, `<files>`, `<read_first>`, `<action>`, `<verify>`, `<acceptance_criteria>`, and `<done>` for `type="auto"` and `type="tracer"` tasks.
+Contains one or more `<task>` elements. Every task element must carry `<name>`, `<files>`, `<read_first>`, `<action>`, `<verify>`, `<acceptance_criteria>`, and `<done>` for `type="auto"` and `type="tracer"` tasks. An optional `<precondition>` element (see [Preconditions](#preconditions)) may sit between `<name>` and `<files>`.
+
+---
+
+## Preconditions
+
+`<precondition>` is an **optional** element on `<task>` (issue #1949, *The Pragmatic Programmer* Topic 23 — Design by Contract). It states, in a single line of runnable/checkable prose, what must already be true for the task to begin safely. It closes the front-of-task side of the contract triad — preconditions (before) ↔ postconditions (`<verify>`/`<done>`/`<acceptance_criteria>`, after) ↔ invariants (`must_haves.truths`, across the whole plan).
+
+```xml
+<task type="auto">
+  <name>Add /reveal endpoint handler</name>
+  <precondition>server bootstraps and responds to GET /health (from the tracer slice)</precondition>
+  <files>server/reveal.ts</files>
+  <action>…</action>
+  <verify>curl /reveal?path=… opens the OS file manager</verify>
+  <done>Endpoint committed and manually verified</done>
+</task>
+```
+
+**Optional and back-compat:** a plan that omits `<precondition>` on every task behaves exactly as today — the executor skips the check with no visible change. Adding `<precondition>` to a task tells the executor to assert it before any other task work (read-only checks only: file existence, env var presence, idempotent health pings; no side-effecting checks — halt and surface a checkpoint if one seems required) and halt (returning a `checkpoint:human-verify`, no partial commit) on an unmet precondition. Plans that include `<precondition>` pass `verify plan-structure` unchanged — the structural validator checks for the presence of required tags and does not reject unknown optional tags.
+
+**Emission cases** (planner-side): emit `<precondition>` only when a task relies on state the plan's own `depends_on` ordering does not already guarantee. Three cases cover every legitimate use:
+
+1. **External service setup** (`user_setup` frontmatter) — the consuming task ties a specific setup step to itself so the executor halts if the setup was skipped.
+2. **Prior-phase artifact dependency** — a generated schema, a migration's dist output, a contract file from an earlier phase. Cross-phase `depends_on` does not cross phase boundaries, so `<precondition>` is the explicit pointer.
+3. **Environment variable / runtime configuration** — a tool, API, or script the task invokes requires an env var or runtime config that exists *now*, not at plan time.
+
+Full emission rules, anti-patterns ("the system is ready" is not checkable; do not use `<precondition>` for intra-plan sequencing — that is what `depends_on` is for), and the contract triad mapping: see `gsd-core/references/planner-preconditions.md`.
 
 ---
 
diff --git a/gsd-core/references/planner-preconditions.md b/gsd-core/references/planner-preconditions.md
new file mode 100644
index 000000000..92cbafd99
--- /dev/null
+++ b/gsd-core/references/planner-preconditions.md
@@ -0,0 +1,156 @@
+# Planner Preconditions — `<precondition>` Element
+
+> Progressive-disclosure reference for `agents/gsd-planner.md`. The planner agent
+> reads this file when it needs the full emission rules for the `<precondition>`
+> task element (issue #1949, *The Pragmatic Programmer* Topic 23 — Design by
+> Contract). The slim pointer in `agents/gsd-planner.md` → `<task_breakdown>`
+> routes here; the canonical schema row lives in `docs/reference/plan-md.md`.
+
+## The contract triad
+
+Every task in a PLAN.md participates in a three-sided contract:
+
+| Contract side | GSD element | When it binds |
+|---|---|---|
+| **Precondition** | `<precondition>` (optional element on `<task>`) | Before the task begins. What must already be true for the task to run safely. |
+| **Postcondition** | `<verify>` + `<done>` + `<acceptance_criteria>` | After the task ends. What the task guarantees on return. |
+| **Invariant** | `must_haves.truths` (plan frontmatter) | Across the whole plan/phase. What always holds. |
+
+GSD already models postconditions and invariants well. `<precondition>` closes
+the missing side: it states, in runnable/checkable terms, what must be true
+*before* a task begins — so an autonomous executor stops the instant an
+assumption is false, instead of building ten atomic commits on top of a
+migration that never ran.
+
+This is the front-of-task companion to the tracer-bullet proposal (#1945):
+tracers prove the *architecture* end-to-end before expansion; preconditions prove
+each expansion task's *assumptions* before it runs. Together they close both ends
+of the "outrunning your headlights" failure mode.
+
+## When to emit `<precondition>`
+
+Emit `<precondition>` ONLY when a task relies on state the plan's own `depends_on`
+ordering does not already guarantee. Three cases cover every legitimate use; if
+the task's prerequisite is intra-plan sequencing, use `depends_on`, NOT
+`<precondition>`.
+
+### Case 1 — External service setup (`user_setup`)
+
+The task depends on an external service the developer must set up (account
+creation, secret retrieval, dashboard configuration, billing activation). The
+`user_setup` frontmatter field already enumerates these steps; `<precondition>`
+on the consuming task ties a specific setup step to a specific task so the
+executor halts if the setup was skipped.
+
+```xml
+<task type="auto">
+  <name>Send welcome email via SendGrid</name>
+  <precondition>SENDGRID_API_KEY is set (user_setup step 1 complete)</precondition>
+  <files>src/email/welcome.ts</files>
+  <action>...</action>
+  <verify>...</verify>
+  <done>Welcome email dispatched for a test user</done>
+</task>
+```
+
+### Case 2 — Prior-phase artifact dependency
+
+The task consumes an artifact a prior phase promised (a generated schema, a
+migration's dist output, a contract file). Cross-phase `depends_on` does not
+cross phase boundaries, so a `<precondition>` is the explicit pointer.
+
+```xml
+<task type="auto">
+  <name>Generate TypeScript client from schema</name>
+  <precondition>dist/schema.json from Phase 02 exists and is non-empty</precondition>
+  <files>src/client/generated.ts</files>
+  <action>...</action>
+  <verify>...</verify>
+  <done>Client generated and compiles</done>
+</task>
+```
+
+### Case 3 — Environment variable / runtime configuration
+
+The task shells out to a tool, hits an API, or runs a script that requires an
+environment variable or runtime config that exists *now* (not at plan time).
+
+```xml
+<task type="auto">
+  <name>Add /reveal endpoint handler</name>
+  <precondition>server bootstraps and responds to GET /health (from the tracer slice)</precondition>
+  <files>server/reveal.ts</files>
+  <action>...</action>
+  <verify>curl /reveal?path=... opens the OS file manager</verify>
+  <done>Endpoint committed and manually verified</done>
+</task>
+```
+
+## Format
+
+`<precondition>` is a single line of prose inside the `<task>` element, placed right after `<name>` and before `<files>`. It is **prose, not a structured block** — concrete enough that the executor agent can run a read-only check (file existence, env var presence, idempotent `GET /health`-style ping), prose enough not to require a parser extension. The executor MUST verify with read-only checks only: no writes, no network POSTs, no secret emission. If a side-effecting check seems required, the executor halts and surfaces a checkpoint rather than running it.
+
+```xml
+<task type="auto">
+  <name>...</name>
+  <precondition>...</precondition>
+  <files>...</files>
+  <action>...</action>
+  <verify>...</verify>
+  <done>...</done>
+</task>
+```
+
+## What NOT to put in a `<precondition>`
+
+- **Vague readiness checks.** "The system is ready" is not checkable. Name the
+  concrete signal: a `curl` response, a file path, an env var name.
+- **Intra-plan ordering.** "Task 1 has completed" — that is what `depends_on`
+  is for. Reserve `<precondition>` for state the plan's wave/dependency graph
+  cannot express.
+- **Implementation choices.** "We have chosen library X" — that belongs in the
+  `<action>` body or a `## Decisions` row, not a runtime fact.
+- **Things the task itself creates.** A precondition names a fact the task
+  *assumes*; if the task produces it, it is a postcondition (`<done>`).
+
+## Executor behavior (assertion contract)
+
+The executor agent reads `<precondition>` before any other task work:
+
+| State | Executor behavior |
+|---|---|
+| **Absent** | No visible change — execute the task exactly as today. Back-compat for every existing plan. |
+| **Met** | No visible change — proceed with the task. The precondition is logged in the SUMMARY only if it was non-trivial to verify. |
+| **Unmet** | STOP — return a `checkpoint:human-verify` (use `checkpoint_return_format`) with `**Blocked by:** Precondition not met: <precondition text>`. Do NOT partial-commit the task. Unmet preconditions are NEVER auto-approved — a missing prerequisite is not a verification step a human can rubber-stamp, it is a fact the executor cannot establish on its own. |
+
+## Plan-structure validation
+
+`cmdVerifyPlanStructure` checks for the presence of required tags (`<name>`,
+`<action>`, etc.) and warns on missing recommended tags (`<verify>`, `<done>`,
+`<files>`). It does **not** reject unknown optional tags, so adding
+`<precondition>` to a plan passes validation unchanged. A future ADR may add
+structured validation if drift emerges; v1 ships prose-only to keep the surface
+minimal (Hyrum's Law: the smaller the observable surface, the less the system
+depends on by accident).
+
+## Out of scope
+
+The following are explicitly NOT part of v1:
+
+- **Structured precondition DSL** (e.g. `<precondition kind="env" var="X"/>`).
+  Prose-first keeps complexity flat; structured validation can land in a later
+  PR if prose proves insufficient.
+- **Automatic precondition emission for every task.** The three cases above are
+  a hard ceiling (Zawinski's Law guard). Most tasks do not need a precondition.
+- **Cross-task preconditions.** A precondition binds one task to one fact. Use
+  `depends_on` or a parent plan's `must_haves` for multi-task contracts.
+
+## See also
+
+- *The Pragmatic Programmer*, Topic 23 — "Design by Contract" (Hunt & Thomas).
+- `docs/reference/plan-md.md` — canonical PLAN.md schema reference (where
+  `<precondition>` appears in the task-element table).
+- Tracer-bullet proposal (#1945) — the architectural-end companion to this
+  front-of-task contract.
+- `agents/gsd-executor.md` → `<execution_flow>` → precondition check step — the
+  assertion surface that consumes what this reference defines.
diff --git a/tests/agent-size-baseline.json b/tests/agent-size-baseline.json
index 11212ff5e..b0b2e09e7 100644
--- a/tests/agent-size-baseline.json
+++ b/tests/agent-size-baseline.json
@@ -14,7 +14,7 @@
   "gsd-domain-researcher.md": 7032,
   "gsd-eval-auditor.md": 12496,
   "gsd-eval-planner.md": 7008,
-  "gsd-executor.md": 45338,
+  "gsd-executor.md": 46644,
   "gsd-framework-selector.md": 6778,
   "gsd-integration-checker.md": 15238,
   "gsd-intel-updater.md": 18166,
@@ -23,7 +23,7 @@
   "gsd-pattern-mapper.md": 12487,
   "gsd-phase-researcher.md": 40866,
   "gsd-plan-checker.md": 44780,
-  "gsd-planner.md": 49314,
+  "gsd-planner.md": 49172,
   "gsd-project-researcher.md": 22242,
   "gsd-research-synthesizer.md": 13847,
   "gsd-roadmapper.md": 22273,
diff --git a/tests/fixtures/golden-install-parity/antigravity.json b/tests/fixtures/golden-install-parity/antigravity.json
index baeb46666..8097d04ea 100644
--- a/tests/fixtures/golden-install-parity/antigravity.json
+++ b/tests/fixtures/golden-install-parity/antigravity.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "1db46cac3f4d9889",
   "agents/gsd-eval-auditor.md": "1b8391f1aafb067f",
   "agents/gsd-eval-planner.md": "3d10fd11147f6857",
-  "agents/gsd-executor.md": "5dc97b2515b36731",
+  "agents/gsd-executor.md": "152955064cf4c9d2",
   "agents/gsd-framework-selector.md": "daa62c79619c76bf",
   "agents/gsd-integration-checker.md": "0643cd2d779b131c",
   "agents/gsd-intel-updater.md": "26c1f1e028c6346a",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "e62ee90d39084802",
   "agents/gsd-phase-researcher.md": "cff1196c8e8bb4fa",
   "agents/gsd-plan-checker.md": "dd1e7cdc837d8f3e",
-  "agents/gsd-planner.md": "c5de6bb9b277e4d4",
+  "agents/gsd-planner.md": "6a442501f9d4caa8",
   "agents/gsd-project-researcher.md": "85de7f562872ee9b",
   "agents/gsd-research-synthesizer.md": "18a2e1b30ff7ae3a",
   "agents/gsd-roadmapper.md": "7a8465ac6d4dd29e",
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "90cb2ecd1f3eb4d8",
   "gsd-core/references/planner-mvp-mode.md": "cdac9dde7cd8fa84",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/augment.json b/tests/fixtures/golden-install-parity/augment.json
index eaab16494..364625d6f 100644
--- a/tests/fixtures/golden-install-parity/augment.json
+++ b/tests/fixtures/golden-install-parity/augment.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "671c9ea949889c4a",
   "agents/gsd-eval-auditor.md": "fcaec7b00f94c435",
   "agents/gsd-eval-planner.md": "a4a5b4b3f7828ba3",
-  "agents/gsd-executor.md": "2df526331a77b2aa",
+  "agents/gsd-executor.md": "47c648f6622e939f",
   "agents/gsd-framework-selector.md": "4b77eebbe9288d80",
   "agents/gsd-integration-checker.md": "fa53e2d78be1de74",
   "agents/gsd-intel-updater.md": "fa40e685d7441ace",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "43c6021cf7caabfa",
   "agents/gsd-phase-researcher.md": "f1f6fd6a3e67c7a8",
   "agents/gsd-plan-checker.md": "bf1a4e636f2390de",
-  "agents/gsd-planner.md": "4614c9f6250d08d4",
+  "agents/gsd-planner.md": "55cc953c6a52ae05",
   "agents/gsd-project-researcher.md": "4531b7cc8f5e5f7d",
   "agents/gsd-research-synthesizer.md": "4a4f68e6c75b133a",
   "agents/gsd-roadmapper.md": "bb2f57695dbab32c",
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "dda0193a0fbd4947",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/claude-local.json b/tests/fixtures/golden-install-parity/claude-local.json
index db988733b..311b0e65c 100644
--- a/tests/fixtures/golden-install-parity/claude-local.json
+++ b/tests/fixtures/golden-install-parity/claude-local.json
@@ -15,7 +15,7 @@
   "agents/gsd-domain-researcher.md": "f1e03df842ddfb95",
   "agents/gsd-eval-auditor.md": "d0f45fff7370bb0b",
   "agents/gsd-eval-planner.md": "9cc049b82897daa4",
-  "agents/gsd-executor.md": "e96f3cbde4428497",
+  "agents/gsd-executor.md": "3c8d4fd1c29542bb",
   "agents/gsd-framework-selector.md": "85005d716f9d98f7",
   "agents/gsd-integration-checker.md": "17a8ee731986564d",
   "agents/gsd-intel-updater.md": "4953a465db9dadc1",
@@ -24,7 +24,7 @@
   "agents/gsd-pattern-mapper.md": "b45b5e106775bec1",
   "agents/gsd-phase-researcher.md": "4772d9eada32e8bd",
   "agents/gsd-plan-checker.md": "75851b147f35354a",
-  "agents/gsd-planner.md": "a5cdb261a6ccbb96",
+  "agents/gsd-planner.md": "4636f48b1b7ca1f6",
   "agents/gsd-project-researcher.md": "d7f355894519f9fe",
   "agents/gsd-research-synthesizer.md": "1c738df9932d325a",
   "agents/gsd-roadmapper.md": "453e9471ad27c7ea",
@@ -185,6 +185,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "add55e135dd968da",
   "gsd-core/references/planner-mvp-mode.md": "98bcd2020c30cbd2",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/claude.json b/tests/fixtures/golden-install-parity/claude.json
index af6265f3f..5f7be45b6 100644
--- a/tests/fixtures/golden-install-parity/claude.json
+++ b/tests/fixtures/golden-install-parity/claude.json
@@ -15,7 +15,7 @@
   "agents/gsd-domain-researcher.md": "5f7d366251b957fe",
   "agents/gsd-eval-auditor.md": "fea2759beff0a642",
   "agents/gsd-eval-planner.md": "112f6730f23854e3",
-  "agents/gsd-executor.md": "e44ea5156ca2a42d",
+  "agents/gsd-executor.md": "e63187a0bbff74eb",
   "agents/gsd-framework-selector.md": "c350ee693cb1aa4e",
   "agents/gsd-integration-checker.md": "c8b4e65dee89c8ea",
   "agents/gsd-intel-updater.md": "5b41e05f90ce89d9",
@@ -24,7 +24,7 @@
   "agents/gsd-pattern-mapper.md": "b45b5e106775bec1",
   "agents/gsd-phase-researcher.md": "85217c69c1ed2ac6",
   "agents/gsd-plan-checker.md": "c70134c61b969589",
-  "agents/gsd-planner.md": "c07a226ddd579839",
+  "agents/gsd-planner.md": "3098091aa1f0756d",
   "agents/gsd-project-researcher.md": "f468e96f8339d1e0",
   "agents/gsd-research-synthesizer.md": "7be02e47f4fd901b",
   "agents/gsd-roadmapper.md": "8a7f1f1256a6aed5",
@@ -114,6 +114,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/cline.json b/tests/fixtures/golden-install-parity/cline.json
index 351f1e12b..84ac13c4e 100644
--- a/tests/fixtures/golden-install-parity/cline.json
+++ b/tests/fixtures/golden-install-parity/cline.json
@@ -19,7 +19,7 @@
   "agents/gsd-domain-researcher.md": "0fecdaea86466a56",
   "agents/gsd-eval-auditor.md": "36c44303085df2f8",
   "agents/gsd-eval-planner.md": "3ddea88a69b4da3f",
-  "agents/gsd-executor.md": "9b51734f64049fda",
+  "agents/gsd-executor.md": "343f7d59b160d74a",
   "agents/gsd-framework-selector.md": "564669d479433f15",
   "agents/gsd-integration-checker.md": "1bbbdd3d420b994e",
   "agents/gsd-intel-updater.md": "42c40fffbc720d0b",
@@ -28,7 +28,7 @@
   "agents/gsd-pattern-mapper.md": "b526065fd2efa19c",
   "agents/gsd-phase-researcher.md": "c507db2ba66038f4",
   "agents/gsd-plan-checker.md": "a609245dbdc4ef2b",
-  "agents/gsd-planner.md": "2fa5c5d4529ef651",
+  "agents/gsd-planner.md": "c2ab476257cd07cf",
   "agents/gsd-project-researcher.md": "049f816c6caa4316",
   "agents/gsd-research-synthesizer.md": "2f7dcbff50371d4c",
   "agents/gsd-roadmapper.md": "bbb23d3097911516",
@@ -118,6 +118,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "e469016f2d51b5bc",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "dda0193a0fbd4947",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/codebuddy.json b/tests/fixtures/golden-install-parity/codebuddy.json
index 301779bca..380fcc5cd 100644
--- a/tests/fixtures/golden-install-parity/codebuddy.json
+++ b/tests/fixtures/golden-install-parity/codebuddy.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "1c1a800108a2b225",
   "agents/gsd-eval-auditor.md": "99012004b14ea602",
   "agents/gsd-eval-planner.md": "4ebdd7fe9cbb0cfe",
-  "agents/gsd-executor.md": "4f4bbb77be53a135",
+  "agents/gsd-executor.md": "44149e405a126f90",
   "agents/gsd-framework-selector.md": "7726fccc86bfeb50",
   "agents/gsd-integration-checker.md": "2d8339790bbb2dc3",
   "agents/gsd-intel-updater.md": "c51339956197cbd3",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "92cfa2e6c2a06bf3",
   "agents/gsd-phase-researcher.md": "6338474da1a5d65e",
   "agents/gsd-plan-checker.md": "e704c083b02e8c35",
-  "agents/gsd-planner.md": "1ade235391742f7e",
+  "agents/gsd-planner.md": "8e3e314f962711cd",
   "agents/gsd-project-researcher.md": "e43c59f7f1f2f37a",
   "agents/gsd-research-synthesizer.md": "87955470c3c129b2",
   "agents/gsd-roadmapper.md": "20b69eff61a7a9fa",
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "dda0193a0fbd4947",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/codex.json b/tests/fixtures/golden-install-parity/codex.json
index a590c9f8f..e4be6d98f 100644
--- a/tests/fixtures/golden-install-parity/codex.json
+++ b/tests/fixtures/golden-install-parity/codex.json
@@ -102,8 +102,8 @@
   "agents/gsd-eval-auditor.toml": "9b81d61b3c5f722d",
   "agents/gsd-eval-planner.md": "73f2ad2ff2797a51",
   "agents/gsd-eval-planner.toml": "09468ad1a34ac468",
-  "agents/gsd-executor.md": "895482e838b13815",
-  "agents/gsd-executor.toml": "a95f6ad24154e646",
+  "agents/gsd-executor.md": "ed8080096522f7ec",
+  "agents/gsd-executor.toml": "126d79d90e2fdf4f",
   "agents/gsd-framework-selector.md": "ebae32430887d2e0",
   "agents/gsd-framework-selector.toml": "637e4e021b7ec380",
   "agents/gsd-integration-checker.md": "9cc875676cf7d741",
@@ -120,8 +120,8 @@
   "agents/gsd-phase-researcher.toml": "44a3d510cd0ce3bd",
   "agents/gsd-plan-checker.md": "e7f02c10ea788aee",
   "agents/gsd-plan-checker.toml": "6f8ceb421d0ad721",
-  "agents/gsd-planner.md": "7d48d3a81760af05",
-  "agents/gsd-planner.toml": "2527d19b0c47ec66",
+  "agents/gsd-planner.md": "cb3ff2ef2c58617c",
+  "agents/gsd-planner.toml": "ac51638704036f71",
   "agents/gsd-project-researcher.md": "959f2e57c3d69ed8",
   "agents/gsd-project-researcher.toml": "f395e8e8c4baf1ed",
   "agents/gsd-research-synthesizer.md": "497f85adf53259ef",
@@ -221,6 +221,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "7889bfa28e82156b",
   "gsd-core/references/planner-revision.md": "2ebf1a714d1ec4bf",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/copilot.json b/tests/fixtures/golden-install-parity/copilot.json
index 7f22b3a69..d0e7cc629 100644
--- a/tests/fixtures/golden-install-parity/copilot.json
+++ b/tests/fixtures/golden-install-parity/copilot.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.agent.md": "d603239b3e9fe428",
   "agents/gsd-eval-auditor.agent.md": "3c03009564de55c8",
   "agents/gsd-eval-planner.agent.md": "14751876fc2b5f16",
-  "agents/gsd-executor.agent.md": "761523a925bd2649",
+  "agents/gsd-executor.agent.md": "e75e46a35b7b260a",
   "agents/gsd-framework-selector.agent.md": "cafeec0b3489be45",
   "agents/gsd-integration-checker.agent.md": "30439b804927acc7",
   "agents/gsd-intel-updater.agent.md": "238c1a886f35a25c",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.agent.md": "b1f488b0fa6a2395",
   "agents/gsd-phase-researcher.agent.md": "03cfb510a766fe93",
   "agents/gsd-plan-checker.agent.md": "c50a5b008ddcbfad",
-  "agents/gsd-planner.agent.md": "2664dc34defa7580",
+  "agents/gsd-planner.agent.md": "8f5f400efea5e446",
   "agents/gsd-project-researcher.agent.md": "d73bdbe986ffa8a6",
   "agents/gsd-research-synthesizer.agent.md": "f03eed4aa89e47c5",
   "agents/gsd-roadmapper.agent.md": "322048cf8ddcb4e5",
@@ -116,6 +116,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "641b6c1ce4dd0c8c",
   "gsd-core/references/planner-mvp-mode.md": "355d8a9ff2b2b67e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/cursor.json b/tests/fixtures/golden-install-parity/cursor.json
index 730759255..cced95471 100644
--- a/tests/fixtures/golden-install-parity/cursor.json
+++ b/tests/fixtures/golden-install-parity/cursor.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "56395dbdabf076f6",
   "agents/gsd-eval-auditor.md": "ad2840fd5cd76172",
   "agents/gsd-eval-planner.md": "2049dac060d00eda",
-  "agents/gsd-executor.md": "68796b76140841c2",
+  "agents/gsd-executor.md": "e3d78836e115b18c",
   "agents/gsd-framework-selector.md": "4b77eebbe9288d80",
   "agents/gsd-integration-checker.md": "5da30584d06b878c",
   "agents/gsd-intel-updater.md": "b8971c5d96e63b38",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "1229c215677f740d",
   "agents/gsd-phase-researcher.md": "982d59921bed463d",
   "agents/gsd-plan-checker.md": "ba51999876d40cf2",
-  "agents/gsd-planner.md": "1feec75fe52b56bd",
+  "agents/gsd-planner.md": "c788d7fb84cf5433",
   "agents/gsd-project-researcher.md": "beeac940d3a10e76",
   "agents/gsd-research-synthesizer.md": "6315f016d55176f4",
   "agents/gsd-roadmapper.md": "d28e7d4bac46dde2",
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/hermes.json b/tests/fixtures/golden-install-parity/hermes.json
index c9eb14893..985d27178 100644
--- a/tests/fixtures/golden-install-parity/hermes.json
+++ b/tests/fixtures/golden-install-parity/hermes.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "412cdbb05ba252ea",
   "agents/gsd-eval-auditor.md": "4ffb265063c318e5",
   "agents/gsd-eval-planner.md": "03448fc9c5774b56",
-  "agents/gsd-executor.md": "c1f807f853dc53d7",
+  "agents/gsd-executor.md": "b70c976372c77dc1",
   "agents/gsd-framework-selector.md": "ea9981d65d6b3429",
   "agents/gsd-integration-checker.md": "35b4f2969d279871",
   "agents/gsd-intel-updater.md": "5fe5edfae2719cb8",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "cea092600aeb3978",
   "agents/gsd-phase-researcher.md": "2bd0402f33d757ca",
   "agents/gsd-plan-checker.md": "4b4e2b475bf5b5c3",
-  "agents/gsd-planner.md": "a48726410b038084",
+  "agents/gsd-planner.md": "d5fa8236f975aacd",
   "agents/gsd-project-researcher.md": "425a7df7f37a5c06",
   "agents/gsd-research-synthesizer.md": "9d31c87fc2c87ffa",
   "agents/gsd-roadmapper.md": "64dce5d5f9fa5654",
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "8f598e08696843c0",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/kilo.json b/tests/fixtures/golden-install-parity/kilo.json
index 6c47ac40b..9583bb9e3 100644
--- a/tests/fixtures/golden-install-parity/kilo.json
+++ b/tests/fixtures/golden-install-parity/kilo.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "a3874d80bcbc7380",
   "agents/gsd-eval-auditor.md": "630d4cd3bd6ea195",
   "agents/gsd-eval-planner.md": "3db12cde12aeb2c1",
-  "agents/gsd-executor.md": "c53d111b0c795f7c",
+  "agents/gsd-executor.md": "73278ea652cac62f",
   "agents/gsd-framework-selector.md": "ad5f2c6b9bec6270",
   "agents/gsd-integration-checker.md": "c503e2f4a3d8ec05",
   "agents/gsd-intel-updater.md": "231393da62a45b2e",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "6a5408fd11d70391",
   "agents/gsd-phase-researcher.md": "94818f28c498bb26",
   "agents/gsd-plan-checker.md": "56164206242c8caf",
-  "agents/gsd-planner.md": "1fbe1f6e9c3b74f0",
+  "agents/gsd-planner.md": "13c4b6db72b6bbb3",
   "agents/gsd-project-researcher.md": "60573a38d3dfd9fe",
   "agents/gsd-research-synthesizer.md": "1f7cd286c5783c86",
   "agents/gsd-roadmapper.md": "277e0a3252553ab7",
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/kimi.json b/tests/fixtures/golden-install-parity/kimi.json
index 3e490e8ca..09e5b64f5 100644
--- a/tests/fixtures/golden-install-parity/kimi.json
+++ b/tests/fixtures/golden-install-parity/kimi.json
@@ -61,7 +61,7 @@
   "agents/subagents/gsd-eval-auditor.yaml": "e3d868bd5fefe938",
   "agents/subagents/gsd-eval-planner.md": "70f8c5727bfb9876",
   "agents/subagents/gsd-eval-planner.yaml": "df8499f7af297ec2",
-  "agents/subagents/gsd-executor.md": "948d122c6607e343",
+  "agents/subagents/gsd-executor.md": "20cf0b2aa886d35c",
   "agents/subagents/gsd-executor.yaml": "e29422986636fd64",
   "agents/subagents/gsd-framework-selector.md": "a15b7aa1e0576e16",
   "agents/subagents/gsd-framework-selector.yaml": "fb52c31cde27b0e3",
@@ -79,7 +79,7 @@
   "agents/subagents/gsd-phase-researcher.yaml": "7633c8e82617e7cc",
   "agents/subagents/gsd-plan-checker.md": "bd302afc01ed40f0",
   "agents/subagents/gsd-plan-checker.yaml": "8295181071121db8",
-  "agents/subagents/gsd-planner.md": "aaaac708b1cf2939",
+  "agents/subagents/gsd-planner.md": "d29376ff9f57cc60",
   "agents/subagents/gsd-planner.yaml": "2e83ee194bcd7fbd",
   "agents/subagents/gsd-project-researcher.md": "39bc2ec5a8b18283",
   "agents/subagents/gsd-project-researcher.yaml": "ce12586b0347e2dc",
@@ -179,6 +179,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "dda0193a0fbd4947",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/opencode.json b/tests/fixtures/golden-install-parity/opencode.json
index d3e63a042..996dd209d 100644
--- a/tests/fixtures/golden-install-parity/opencode.json
+++ b/tests/fixtures/golden-install-parity/opencode.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "71250e759ca9e723",
   "agents/gsd-eval-auditor.md": "c88890105f32ace6",
   "agents/gsd-eval-planner.md": "60bddb70a937f796",
-  "agents/gsd-executor.md": "4f180ee85214abe8",
+  "agents/gsd-executor.md": "84c0a7dc19ddb6c5",
   "agents/gsd-framework-selector.md": "1c0a10355e787675",
   "agents/gsd-integration-checker.md": "a9de5928e5a5c649",
   "agents/gsd-intel-updater.md": "493e07482fa6198a",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "7c6d1d9817a9c1e7",
   "agents/gsd-phase-researcher.md": "9874110700b41f48",
   "agents/gsd-plan-checker.md": "28ca3dc43669894f",
-  "agents/gsd-planner.md": "4e568338c7ee6b80",
+  "agents/gsd-planner.md": "87d1aa910eb02ad5",
   "agents/gsd-project-researcher.md": "dae210ae0b3c6e2b",
   "agents/gsd-research-synthesizer.md": "e02c6ad5d1b74171",
   "agents/gsd-roadmapper.md": "1658a40b20d8b575",
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "97f6e67b56c072c1",
   "gsd-core/references/planner-mvp-mode.md": "35d30284ea9110c0",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/pi.json b/tests/fixtures/golden-install-parity/pi.json
index b87f500f2..30bf878f2 100644
--- a/tests/fixtures/golden-install-parity/pi.json
+++ b/tests/fixtures/golden-install-parity/pi.json
@@ -82,6 +82,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "dda0193a0fbd4947",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/qwen.json b/tests/fixtures/golden-install-parity/qwen.json
index 3217ff6d3..1514e33cf 100644
--- a/tests/fixtures/golden-install-parity/qwen.json
+++ b/tests/fixtures/golden-install-parity/qwen.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "bd054bb27beed2a7",
   "agents/gsd-eval-auditor.md": "57cc7458ab5de6b7",
   "agents/gsd-eval-planner.md": "01b665728dde4ccf",
-  "agents/gsd-executor.md": "988960899bd49c68",
+  "agents/gsd-executor.md": "6dcccfef842a49ac",
   "agents/gsd-framework-selector.md": "82ba6abea84226b7",
   "agents/gsd-integration-checker.md": "90835dbc7dfa1691",
   "agents/gsd-intel-updater.md": "3cc4f6ddd04676ec",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "83c66c7722e8b165",
   "agents/gsd-phase-researcher.md": "284e55a86ae46d7f",
   "agents/gsd-plan-checker.md": "c8a8fcc8ed38eff0",
-  "agents/gsd-planner.md": "75989c686d191143",
+  "agents/gsd-planner.md": "f0a5bede90f23be4",
   "agents/gsd-project-researcher.md": "b5baac64a15c85e2",
   "agents/gsd-research-synthesizer.md": "6cd9b501dc97bd50",
   "agents/gsd-roadmapper.md": "c357a77ab919e9e5",
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "3f6f5ee62d86f72d",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/trae.json b/tests/fixtures/golden-install-parity/trae.json
index b32df012d..2734968b7 100644
--- a/tests/fixtures/golden-install-parity/trae.json
+++ b/tests/fixtures/golden-install-parity/trae.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "b80f76874c04e515",
   "agents/gsd-eval-auditor.md": "470bf16303ec4d2e",
   "agents/gsd-eval-planner.md": "22334fde85723c9d",
-  "agents/gsd-executor.md": "2e92d53ec70b614f",
+  "agents/gsd-executor.md": "b3baa767abac0593",
   "agents/gsd-framework-selector.md": "7726fccc86bfeb50",
   "agents/gsd-integration-checker.md": "7cd2072984411c7f",
   "agents/gsd-intel-updater.md": "83de6ba9172891c3",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "b5d7a4abb1baecb9",
   "agents/gsd-phase-researcher.md": "2256f1f82212c757",
   "agents/gsd-plan-checker.md": "523119bd5d6599fe",
-  "agents/gsd-planner.md": "3cbce9388340c855",
+  "agents/gsd-planner.md": "fb330c599b9c1dac",
   "agents/gsd-project-researcher.md": "ddf7794e81300032",
   "agents/gsd-research-synthesizer.md": "a124b00271748d07",
   "agents/gsd-roadmapper.md": "493ef92b42b12cf4",
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "9a9383599893ea7e",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/windsurf.json b/tests/fixtures/golden-install-parity/windsurf.json
index 63727749a..4aa8487a5 100644
--- a/tests/fixtures/golden-install-parity/windsurf.json
+++ b/tests/fixtures/golden-install-parity/windsurf.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "56395dbdabf076f6",
   "agents/gsd-eval-auditor.md": "fb64fc5acf359747",
   "agents/gsd-eval-planner.md": "2049dac060d00eda",
-  "agents/gsd-executor.md": "5d56ba16562745d0",
+  "agents/gsd-executor.md": "45c4632bc67a12a2",
   "agents/gsd-framework-selector.md": "4b77eebbe9288d80",
   "agents/gsd-integration-checker.md": "4ffb37fb230c2b90",
   "agents/gsd-intel-updater.md": "a81d77c143c02108",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "ada0c169daa2f0ec",
   "agents/gsd-phase-researcher.md": "2a45ebde829555ec",
   "agents/gsd-plan-checker.md": "33fbf70b7b24eb1e",
-  "agents/gsd-planner.md": "c4072a4678c17485",
+  "agents/gsd-planner.md": "61ac0bd59b5b836a",
   "agents/gsd-project-researcher.md": "f6697b316b5995ba",
   "agents/gsd-research-synthesizer.md": "04036f38c1d373ea",
   "agents/gsd-roadmapper.md": "fb62e1e3de84b5f9",
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "18d50b6d12db830e",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "da39eace09a10743",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/golden-install-parity/zcode.json b/tests/fixtures/golden-install-parity/zcode.json
index 056cd7184..5e498dae7 100644
--- a/tests/fixtures/golden-install-parity/zcode.json
+++ b/tests/fixtures/golden-install-parity/zcode.json
@@ -16,7 +16,7 @@
   "agents/gsd-domain-researcher.md": "049f588663814fa2",
   "agents/gsd-eval-auditor.md": "54870d3b07433525",
   "agents/gsd-eval-planner.md": "552e9fa164c51ce8",
-  "agents/gsd-executor.md": "b49a6d92b2cd9831",
+  "agents/gsd-executor.md": "59fbb1e047b9a7c4",
   "agents/gsd-framework-selector.md": "8a795f230436ad2e",
   "agents/gsd-integration-checker.md": "c1760a0bbd4f7bf5",
   "agents/gsd-intel-updater.md": "944f1d903e2e9e09",
@@ -25,7 +25,7 @@
   "agents/gsd-pattern-mapper.md": "68ecefd60811a669",
   "agents/gsd-phase-researcher.md": "2235f61764d8e969",
   "agents/gsd-plan-checker.md": "bb38f345d3d41edc",
-  "agents/gsd-planner.md": "e76def94ab518216",
+  "agents/gsd-planner.md": "42f6e9832d5c2edc",
   "agents/gsd-project-researcher.md": "f572892f138734ff",
   "agents/gsd-research-synthesizer.md": "29949bf3f049a8f1",
   "agents/gsd-roadmapper.md": "840ac933e3b094f9",
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md": "b28fa3da6ae739a8",
   "gsd-core/references/planner-load-graph-context.md": "ca7a7af3f35ae61b",
   "gsd-core/references/planner-mvp-mode.md": "cfd535c9c545e73e",
+  "gsd-core/references/planner-preconditions.md": "4511829607ec9107",
   "gsd-core/references/planner-reviews.md": "dda0193a0fbd4947",
   "gsd-core/references/planner-revision.md": "86ba8a511f081f05",
   "gsd-core/references/planner-source-audit.md": "7de5bdb07232ce0b",
diff --git a/tests/fixtures/install-tree/antigravity.json b/tests/fixtures/install-tree/antigravity.json
index 310ffad32..18cf446a0 100644
--- a/tests/fixtures/install-tree/antigravity.json
+++ b/tests/fixtures/install-tree/antigravity.json
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/augment.json b/tests/fixtures/install-tree/augment.json
index a4b2e7922..de408512c 100644
--- a/tests/fixtures/install-tree/augment.json
+++ b/tests/fixtures/install-tree/augment.json
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/claude-local.json b/tests/fixtures/install-tree/claude-local.json
index 2f060468e..abd55e82d 100644
--- a/tests/fixtures/install-tree/claude-local.json
+++ b/tests/fixtures/install-tree/claude-local.json
@@ -185,6 +185,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/claude.json b/tests/fixtures/install-tree/claude.json
index f0920a02e..39b9c7780 100644
--- a/tests/fixtures/install-tree/claude.json
+++ b/tests/fixtures/install-tree/claude.json
@@ -114,6 +114,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/cline.json b/tests/fixtures/install-tree/cline.json
index be4c9c39e..36a075671 100644
--- a/tests/fixtures/install-tree/cline.json
+++ b/tests/fixtures/install-tree/cline.json
@@ -118,6 +118,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/codebuddy.json b/tests/fixtures/install-tree/codebuddy.json
index fd8ed7e53..d4f673042 100644
--- a/tests/fixtures/install-tree/codebuddy.json
+++ b/tests/fixtures/install-tree/codebuddy.json
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/codex.json b/tests/fixtures/install-tree/codex.json
index d6f76ea04..cc170128b 100644
--- a/tests/fixtures/install-tree/codex.json
+++ b/tests/fixtures/install-tree/codex.json
@@ -221,6 +221,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/copilot.json b/tests/fixtures/install-tree/copilot.json
index d7f1e3824..6b5df9763 100644
--- a/tests/fixtures/install-tree/copilot.json
+++ b/tests/fixtures/install-tree/copilot.json
@@ -116,6 +116,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/cursor.json b/tests/fixtures/install-tree/cursor.json
index 2e3fa2eb1..a30363bca 100644
--- a/tests/fixtures/install-tree/cursor.json
+++ b/tests/fixtures/install-tree/cursor.json
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/hermes.json b/tests/fixtures/install-tree/hermes.json
index 58acc1d33..925431378 100644
--- a/tests/fixtures/install-tree/hermes.json
+++ b/tests/fixtures/install-tree/hermes.json
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/kilo.json b/tests/fixtures/install-tree/kilo.json
index 19c0fbe5d..4521e6168 100644
--- a/tests/fixtures/install-tree/kilo.json
+++ b/tests/fixtures/install-tree/kilo.json
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/kimi.json b/tests/fixtures/install-tree/kimi.json
index 100fc69eb..9f2615ec9 100644
--- a/tests/fixtures/install-tree/kimi.json
+++ b/tests/fixtures/install-tree/kimi.json
@@ -179,6 +179,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/opencode.json b/tests/fixtures/install-tree/opencode.json
index ca22c4048..330121e16 100644
--- a/tests/fixtures/install-tree/opencode.json
+++ b/tests/fixtures/install-tree/opencode.json
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/pi.json b/tests/fixtures/install-tree/pi.json
index 677542e14..4baae4984 100644
--- a/tests/fixtures/install-tree/pi.json
+++ b/tests/fixtures/install-tree/pi.json
@@ -82,6 +82,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/qwen.json b/tests/fixtures/install-tree/qwen.json
index 4a6132ada..041cd1410 100644
--- a/tests/fixtures/install-tree/qwen.json
+++ b/tests/fixtures/install-tree/qwen.json
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/trae.json b/tests/fixtures/install-tree/trae.json
index 3bff0d1ff..b48ca07e4 100644
--- a/tests/fixtures/install-tree/trae.json
+++ b/tests/fixtures/install-tree/trae.json
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/windsurf.json b/tests/fixtures/install-tree/windsurf.json
index e73fbe5cd..0054b2e3c 100644
--- a/tests/fixtures/install-tree/windsurf.json
+++ b/tests/fixtures/install-tree/windsurf.json
@@ -115,6 +115,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/fixtures/install-tree/zcode.json b/tests/fixtures/install-tree/zcode.json
index ad72e0ff6..fa6044c57 100644
--- a/tests/fixtures/install-tree/zcode.json
+++ b/tests/fixtures/install-tree/zcode.json
@@ -186,6 +186,7 @@
   "gsd-core/references/planner-interface-context.md",
   "gsd-core/references/planner-load-graph-context.md",
   "gsd-core/references/planner-mvp-mode.md",
+  "gsd-core/references/planner-preconditions.md",
   "gsd-core/references/planner-reviews.md",
   "gsd-core/references/planner-revision.md",
   "gsd-core/references/planner-source-audit.md",
diff --git a/tests/precondition-element.test.cjs b/tests/precondition-element.test.cjs
new file mode 100644
index 000000000..b1b6c2992
--- /dev/null
+++ b/tests/precondition-element.test.cjs
@@ -0,0 +1,233 @@
+// allow-test-rule: source-text-is-the-product [#1949]
+// Agent .md, reference .md, and docs/reference/*.md files — their text IS what the
+// runtime loads. Per CONTRIBUTING.md exception matrix, asserting these files
+// document the <precondition> contract tests the deployed surface, not derived
+// behavior. The behavioral test (cmdVerifyPlanStructure) asserts the validator
+// stays additive. Issue #1949.
+
+'use strict';
+
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const { runGsdTools, createTempProject, cleanup } = require('./helpers.cjs');
+
+const ROOT = path.resolve(__dirname, '..');
+const PLANNER = path.join(ROOT, 'agents', 'gsd-planner.md');
+const EXECUTOR = path.join(ROOT, 'agents', 'gsd-executor.md');
+const PLAN_MD_DOC = path.join(ROOT, 'docs', 'reference', 'plan-md.md');
+const PRECONDITIONS_REF = path.join(ROOT, 'gsd-core', 'references', 'planner-preconditions.md');
+
+function read(rel) {
+  return fs.readFileSync(rel, 'utf-8').replace(/\r\n/g, '\n').replace(/\r/g, '\n');
+}
+
+// ─── Schema documentation (docs/reference/plan-md.md) ────────────────────────
+
+describe('issue #1949: plan-md.md documents <precondition>', () => {
+  test('plan-md.md mentions <precondition> as an optional task element', () => {
+    const doc = read(PLAN_MD_DOC);
+    assert.match(
+      doc,
+      /<precondition>/,
+      'docs/reference/plan-md.md must document the <precondition> element'
+    );
+  });
+
+  test('plan-md.md states <precondition> is optional and does not break plans that omit it', () => {
+    const doc = read(PLAN_MD_DOC);
+    assert.ok(
+      /optional/.test(doc) && /precondition/.test(doc),
+      'plan-md.md must describe <precondition> as optional'
+    );
+  });
+});
+
+// ─── Planner emission contract (agents/gsd-planner.md) ──────────────────────
+
+describe('issue #1949: gsd-planner.md declares <precondition> emission', () => {
+  test('planner references the precondition reference file', () => {
+    const planner = read(PLANNER);
+    assert.ok(
+      planner.includes('planner-preconditions.md'),
+      'gsd-planner.md must @-reference planner-preconditions.md (progressive disclosure)'
+    );
+  });
+
+  test('planner is under the 49152-char cap after adding <precondition> content', () => {
+    const planner = read(PLANNER);
+    assert.ok(
+      planner.length < 49152,
+      `gsd-planner.md is ${planner.length} chars, must be < 49152 (LF-normalized)`
+    );
+  });
+});
+
+// ─── Planner-preconditions reference file (progressive disclosure) ───────────
+
+describe('issue #1949: planner-preconditions.md exists with the three emission cases', () => {
+  test('reference file exists', () => {
+    assert.ok(fs.existsSync(PRECONDITIONS_REF), `Missing: ${PRECONDITIONS_REF}`);
+  });
+
+  test('reference documents the user_setup emission case', () => {
+    const ref = read(PRECONDITIONS_REF);
+    assert.ok(
+      /user_setup/.test(ref) || /external service setup/i.test(ref),
+      'planner-preconditions.md must document the user_setup / external-setup emission case'
+    );
+  });
+
+  test('reference documents the prior-phase artifact emission case', () => {
+    const ref = read(PRECONDITIONS_REF);
+    assert.ok(
+      /prior.?phase artifact/i.test(ref) || /artifact from (a )?prior/i.test(ref),
+      'planner-preconditions.md must document the prior-phase-artifact emission case'
+    );
+  });
+
+  test('reference documents the env-var emission case', () => {
+    const ref = read(PRECONDITIONS_REF);
+    assert.ok(
+      /env(ironment)? var/i.test(ref),
+      'planner-preconditions.md must document the env-var emission case'
+    );
+  });
+
+  test('reference maps the contract triad (precondition / postcondition / invariant)', () => {
+    const ref = read(PRECONDITIONS_REF);
+    assert.ok(
+      /postcondition|<verify>|<done>/.test(ref),
+      'planner-preconditions.md must map <precondition> to existing postconditions (<verify>/<done>)'
+    );
+  });
+});
+
+// ─── Executor assertion contract (agents/gsd-executor.md) ────────────────────
+
+describe('issue #1949: gsd-executor.md asserts <precondition> before task execution', () => {
+  test('executor mentions <precondition>', () => {
+    const exec = read(EXECUTOR);
+    assert.match(
+      exec,
+      /<precondition>/,
+      'gsd-executor.md must reference <precondition>'
+    );
+  });
+
+  test('executor routes an unmet precondition through checkpoint machinery (halt, no partial commit)', () => {
+    const exec = read(EXECUTOR);
+    assert.ok(
+      /precondition/i.test(exec) && /checkpoint/.test(exec),
+      'gsd-executor.md must route unmet <precondition> through checkpoint machinery'
+    );
+  });
+
+  test('executor treats a met/absent precondition as a no-op (does not change flow)', () => {
+    const exec = read(EXECUTOR);
+    assert.ok(
+      /no.op|no visible change|continue/i.test(exec),
+      'gsd-executor.md must state that a met or absent precondition produces no visible change'
+    );
+  });
+
+  test('executor is under the 49152-char cap after adding <precondition> content', () => {
+    const exec = read(EXECUTOR);
+    assert.ok(
+      exec.length < 49152,
+      `gsd-executor.md is ${exec.length} chars, must be < 49152 (LF-normalized)`
+    );
+  });
+});
+
+// ─── Behavioral test: validator stays additive (cmdVerifyPlanStructure) ──────
+//
+// `cmdVerifyPlanStructure` checks for PRESENCE of required tags. It must not
+// reject unknown optional tags. This is the "does not break plans that omit it"
+// plus "does not break plans that include it" guarantee from acceptance #1.
+// Pattern mirrors tests/tracer-bullet.test.cjs (companion feature #1945).
+
+function planWith({ precondition = null } = {}) {
+  const lines = [
+    '<task type="auto">',
+    '  <name>Task 1: Test</name>',
+  ];
+  if (precondition !== null) {
+    lines.push(`  <precondition>${precondition}</precondition>`);
+  }
+  lines.push(
+    '  <files>src/x.ts</files>',
+    '  <action>Do the thing.</action>',
+    '  <verify><automated>echo ok</automated></verify>',
+    '  <done>Done</done>',
+    '</task>',
+    '',
+  );
+  return [
+    '---',
+    'phase: 01-test',
+    'plan: 01',
+    'type: execute',
+    'wave: 1',
+    'depends_on: []',
+    'files_modified: [src/x.ts]',
+    'autonomous: true',
+    'must_haves:',
+    '  truths:',
+    '    - "something is true"',
+    '---',
+    '',
+    '<tasks>',
+    '',
+    ...lines,
+    '</tasks>',
+  ].join('\n');
+}
+
+function verifyPlan(tmpDir, content) {
+  const rel = path.join('.planning', 'phases', '01-test', '01-01-PLAN.md');
+  fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-test'), { recursive: true });
+  fs.writeFileSync(path.join(tmpDir, rel), content);
+  const result = runGsdTools(`verify plan-structure ${rel}`, tmpDir);
+  assert.ok(result.success, `verify plan-structure failed to run: ${result.error}`);
+  return JSON.parse(result.output);
+}
+
+describe('issue #1949: cmdVerifyPlanStructure accepts <precondition> (additive)', () => {
+  test('plan with <precondition> passes structural validation', (t) => {
+    const tmp = createTempProject();
+    t.after(() => cleanup(tmp));
+
+    const out = verifyPlan(tmp, planWith({ precondition: 'OPENAI_API_KEY is set in the environment' }));
+    assert.strictEqual(out.valid, true, `plan with <precondition> must be valid, errors: ${JSON.stringify(out.errors)}`);
+    assert.deepStrictEqual(out.errors, [], 'no validation path may reject a <precondition> task');
+    assert.ok(
+      !(out.warnings || []).some((w) => /precondition/i.test(w)),
+      'nothing may flag the <precondition> element specifically',
+    );
+  });
+
+  test('plan without <precondition> still passes structural validation (back-compat)', (t) => {
+    const tmp = createTempProject();
+    t.after(() => cleanup(tmp));
+
+    const out = verifyPlan(tmp, planWith({ precondition: null }));
+    assert.strictEqual(out.valid, true, `plan without <precondition> must be valid (back-compat), errors: ${JSON.stringify(out.errors)}`);
+  });
+});
+
+// ─── Parity: docs/reference/plan-md.md and planner-preconditions.md agree ────
+//
+// DEFECT.GENERATIVE-FIX-DIVERGENCE: two surfaces describing the same schema
+// must agree on the canonical tag spelling. This is the parity guard against
+// silent drift.
+
+describe('issue #1949: parity between plan-md.md and planner-preconditions.md', () => {
+  test('both surfaces spell the canonical tag <precondition>', () => {
+    const doc = read(PLAN_MD_DOC);
+    const ref = read(PRECONDITIONS_REF);
+    assert.ok(doc.includes('<precondition>'), 'plan-md.md must spell <precondition>');
+    assert.ok(ref.includes('<precondition>'), 'planner-preconditions.md must spell <precondition>');
+  });
+});