diff --git a/.changeset/curious-birds-dance.md b/.changeset/curious-birds-dance.md
new file mode 100644
index 000000000..74673963b
--- /dev/null
+++ b/.changeset/curious-birds-dance.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 4019
+---
+**`workflow.inline_plan_threshold` now has one default owner** — the key is registered in the defaults manifest (default `2`), so `config-get` resolves the absent key instead of erroring, `settings-advanced` no longer misdocuments the default as 3, and every shipped surface (workflow fallback, reference tables) agrees. (#3801)
diff --git a/gsd-core/bin/shared/config-defaults.manifest.json b/gsd-core/bin/shared/config-defaults.manifest.json
index eb443f9f7..164b4ac5d 100644
--- a/gsd-core/bin/shared/config-defaults.manifest.json
+++ b/gsd-core/bin/shared/config-defaults.manifest.json
@@ -1,5 +1,5 @@
 {
-  "_comment": "Canonical CONFIG_DEFAULTS for the Configuration Module. Nested shape is canonical. CJS flat projection (branching_strategy, sub_repos, etc.) is handled by consumers at the boundary. Security keys (security_enforcement, security_asvs_level, security_block_on) and post_planning_gaps live in workflow.* as their canonical location. resolve_model_ids, context_window, phase_naming are CJS-originated top-level keys included here. brave_search, firecrawl, exa_search default to false in the manifest; at runtime buildNewProjectConfig detects API keys. The plan_checker (CJS flat) → workflow.plan_check (canonical nested) divergence is resolved: canonical name is workflow.plan_check. _auto_chain_active is a runtime-state field included for completeness.",
+  "_comment": "Canonical CONFIG_DEFAULTS for the Configuration Module. Nested shape is canonical. CJS flat projection (branching_strategy, sub_repos, etc.) is handled by consumers at the boundary. Security keys (security_enforcement, security_asvs_level, security_block_on) and post_planning_gaps live in workflow.* as their canonical location. resolve_model_ids, context_window, phase_naming are CJS-originated top-level keys included here. brave_search, firecrawl, exa_search default to false in the manifest; at runtime buildNewProjectConfig detects API keys. The plan_checker (CJS flat) \u2192 workflow.plan_check (canonical nested) divergence is resolved: canonical name is workflow.plan_check. _auto_chain_active is a runtime-state field included for completeness.",
   "model_profile": "balanced",
   "commit_docs": true,
   "parallelization": true,
@@ -52,6 +52,7 @@
     "plan_bounce": false,
     "plan_bounce_script": null,
     "plan_bounce_passes": 2,
+    "inline_plan_threshold": 2,
     "auto_prune_state": false,
     "post_planning_gaps": true,
     "security_enforcement": true,
diff --git a/gsd-core/references/planning-config.md b/gsd-core/references/planning-config.md
index e44d9933c..2e83ec22d 100644
--- a/gsd-core/references/planning-config.md
+++ b/gsd-core/references/planning-config.md
@@ -38,6 +38,7 @@ Configuration options for `.planning/` directory behavior.
 | `git.quick_branch_template` | `null` | Optional branch template for quick-task runs |
 | `workflow.use_worktrees` | `true` | Whether executor agents run in isolated git worktrees. Set to `false` to disable worktrees — agents execute sequentially on the main working tree instead. Recommended for solo developers or when worktree merges cause issues. Note: if your branch is ahead of `origin/HEAD` (a diverged milestone or feature branch), GSD auto-degrades to sequential and prints a warning; set `worktree.baseRef:"head"` in `.claude/settings.local.json` to restore parallel execution. See the branch-divergence note below. |
 | `workflow.subagent_timeout` | `300000` | Timeout in milliseconds for parallel subagent tasks (e.g. codebase mapping). Increase for large codebases or slower models. Default: 300000 (5 minutes). |
+| `workflow.inline_plan_threshold` | `2` | Plans with this many tasks or fewer execute inline (Pattern C) instead of spawning a subagent. Avoids ~14K token spawn overhead for small plans. Set to `0` to always spawn subagents. |
 | `workflow.test_command` | `null` | Custom shell command run as the regression/test gate by execute-phase, audit-fix, and post-merge-gate. When unset, GSD auto-detects (Makefile / package.json / Cargo.toml / go.mod / pyproject.toml). Example: `npm test`. |
 | `workflow.build_command` | `null` | Custom shell command run as the build gate by the post-merge gate. When unset, the build step is skipped/auto-detected. Example: `npm run build`. |
 | `workflow.inline_plan_threshold` | `2` | Plans with this many tasks or fewer execute inline (Pattern C) instead of spawning a subagent. Avoids ~14K token spawn overhead for small plans. Set to `0` to always spawn subagents. |
@@ -271,6 +272,7 @@ Set via `workflow.*` namespace in config.json (e.g., `"workflow": { "research":
 | `workflow.skip_discuss` | boolean | `false` | `true`, `false` | Skip discuss phase entirely |
 | `workflow.use_worktrees` | boolean | `true` | `true`, `false` | Run executor agents in isolated git worktrees |
 | `workflow.subagent_timeout` | number | `300000` | Any positive integer (ms) | Timeout for parallel subagent tasks (default: 5 minutes) |
+| `workflow.inline_plan_threshold` | number | `2` | `0`–`10` | Plans with ≤N tasks execute inline instead of spawning a subagent |
 | `workflow.test_command` | string\|null | `null` | Any shell command | Regression/test gate command run by execute-phase, audit-fix, and post-merge-gate. Unset → GSD auto-detects (Makefile / package.json / Cargo.toml / go.mod / pyproject.toml). |
 | `workflow.build_command` | string\|null | `null` | Any shell command | Build gate command run by the post-merge gate. Unset → build step auto-detected/skipped. |
 | `workflow.mvp_mode` | boolean | `false` | `true`, `false` | Persist the MVP-mode flag in config so every phase defaults to MVP framing without requiring `--mvp` on the CLI. Resolved via the chain: `--mvp` CLI flag → ROADMAP.md `**Mode:** mvp` field → this config value → `false`. When `true`, the planner, executor, verifier, and discovery surfaces (progress, stats, graphify) all treat the phase as an MVP vertical slice (UI → API → DB) of one user-visible capability. |
diff --git a/gsd-core/workflows/settings-advanced.md b/gsd-core/workflows/settings-advanced.md
index efc935cd9..1ad7b733f 100644
--- a/gsd-core/workflows/settings-advanced.md
+++ b/gsd-core/workflows/settings-advanced.md
@@ -51,7 +51,7 @@ Planning Tuning:
 - `workflow.plan_bounce_passes` (default: `2`)
 - `workflow.plan_bounce_script` (default: `null`)
 - `workflow.subagent_timeout` (default: `300000`)
-- `workflow.inline_plan_threshold` (default: `3`)
+- `workflow.inline_plan_threshold` (default: `2`)
 
 Execution Tuning:
 - `workflow.node_repair` (default: `true`)
diff --git a/src/config-loader.cts b/src/config-loader.cts
index c3bd4748a..4e3af331d 100644
--- a/src/config-loader.cts
+++ b/src/config-loader.cts
@@ -134,6 +134,7 @@ const CONFIG_DEFAULTS = {
   security_block_on: _getNestedConfigDefault('workflow', 'security_block_on'),
   post_planning_gaps: _getNestedConfigDefault('workflow', 'post_planning_gaps'),
   smart_zone_tokens: _getNestedConfigDefault('workflow', 'smart_zone_tokens'),
+  inline_plan_threshold: _getNestedConfigDefault('workflow', 'inline_plan_threshold'), // #3801
   max_prompt_tokens: _getNestedConfigDefault('review', 'max_prompt_tokens'),
 };
 
diff --git a/src/config.cts b/src/config.cts
index 1b85906d9..94a75a81e 100644
--- a/src/config.cts
+++ b/src/config.cts
@@ -111,6 +111,11 @@ const SCHEMA_DEFAULTS: Record<string, unknown> = {
   // manifest default rather than "Key not found". Derived from the defaults manifest so
   // the manifest stays the single source of truth.
   'planning.pr_strict': CONFIG_DEFAULTS.pr_strict,
+  // #3801: execute-plan reads this key on every run; an absent key must resolve
+  // to the manifest default (2) rather than "Key not Found" — previously the
+  // effective default existed only as the workflow's shell fallback and the
+  // docs disagreed (settings-advanced said 3). Manifest stays the one owner.
+  'workflow.inline_plan_threshold': CONFIG_DEFAULTS.inline_plan_threshold,
 };
 
 /**
diff --git a/tests/config-field-docs.test.cjs b/tests/config-field-docs.test.cjs
index a08772c23..b2c74b700 100644
--- a/tests/config-field-docs.test.cjs
+++ b/tests/config-field-docs.test.cjs
@@ -105,6 +105,7 @@ describe('config-field-docs', () => {
       security_enforcement: 'workflow.security_enforcement',
       security_asvs_level: 'workflow.security_asvs_level',
       security_block_on: 'workflow.security_block_on',
+      inline_plan_threshold: 'workflow.inline_plan_threshold', // #3801
     };
 
     const missing = keys.filter(k => {
diff --git a/tests/inline-plan-threshold-default.test.cjs b/tests/inline-plan-threshold-default.test.cjs
new file mode 100644
index 000000000..45ff6c7ba
--- /dev/null
+++ b/tests/inline-plan-threshold-default.test.cjs
@@ -0,0 +1,65 @@
+'use strict';
+
+// ─────────────────────────────────────────────────────────────────────────────
+// #3801 — workflow.inline_plan_threshold's default must have ONE owner.
+//
+// The effective default existed only as execute-plan.md's shell fallback
+// (`|| echo "2"`); the key was never registered in
+// config-defaults.manifest.json, and settings-advanced.md documented the
+// default as 3. This guard pins: the manifest OWNS the default (key present,
+// value 2), every shipped doc that names a default agrees with the manifest,
+// and the shell fallbacks agree too.
+// ─────────────────────────────────────────────────────────────────────────────
+
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+
+const REPO = path.join(__dirname, '..');
+const MANIFEST = JSON.parse(fs.readFileSync(
+  path.join(REPO, 'gsd-core', 'bin', 'shared', 'config-defaults.manifest.json'),
+  'utf8',
+));
+
+test('#3801: the defaults manifest owns workflow.inline_plan_threshold (default 2)', () => {
+  assert.ok(
+    MANIFEST.workflow && Object.prototype.hasOwnProperty.call(MANIFEST.workflow, 'inline_plan_threshold'),
+    'the key must be registered in config-defaults.manifest.json — one source of truth',
+  );
+  assert.strictEqual(MANIFEST.workflow.inline_plan_threshold, 2);
+});
+
+test('#3801: every shipped surface naming the default agrees with the manifest', () => {
+  const surfaces = [
+    ['gsd-core/workflows/settings-advanced.md', /inline_plan_threshold`\s*\(default:\s*`(\d+)`/],
+  ];
+  for (const [rel, re] of surfaces) {
+    const md = fs.readFileSync(path.join(REPO, rel), 'utf8');
+    const m = re.exec(md);
+    assert.ok(m, `${rel} must name the inline_plan_threshold default`);
+    assert.strictEqual(m[1], '2', `#3801: ${rel} documents the default as ${m[1]} — must agree with the manifest's 2`);
+  }
+  // planning-config.md's two tables are read via the shared markdown-table
+  // parser (parseMarkdownTable), not an ad-hoc cell regex.
+  const { parseMarkdownTable } = require('../gsd-core/bin/lib/markdown-table.cjs');
+  const pc = fs.readFileSync(path.join(REPO, 'gsd-core', 'references', 'planning-config.md'), 'utf8');
+  const parsed = parseMarkdownTable(pc);
+  assert.ok(parsed.ok, 'planning-config.md must contain a parseable defaults table');
+  const defaultsTable = parsed.value;
+  const thresholdRows = defaultsTable.rows.filter((r) => String(r['Option']).includes('inline_plan_threshold'));
+  assert.ok(thresholdRows.length >= 1, 'planning-config.md must document inline_plan_threshold');
+  for (const row of thresholdRows) {
+    const def = String(row['Default']).replace(/`/g, '').trim();
+    assert.strictEqual(def, '2', `#3801: planning-config.md documents the default as ${def} — must agree with the manifest's 2`);
+  }
+  // The execute-plan prose default and the shell fallback both say 2.
+  const ep = fs.readFileSync(path.join(REPO, 'gsd-core', 'workflows', 'execute-plan.md'), 'utf8');
+  // The shell-fallback line is matched with a pipe-free, CRLF-safe pattern.
+  const { splitLines } = require('../gsd-core/bin/lib/text-lines.cjs');
+  const fallbackLine = splitLines(ep).find((l) => l.includes('config-get workflow.inline_plan_threshold'));
+  assert.ok(fallbackLine, 'execute-plan.md must fetch the key');
+  assert.ok(fallbackLine.includes('echo "2"'),
+    `the shell fallback must agree with the manifest default; got ${fallbackLine}`);
+  assert.match(ep, /default: 2, set to `0` to always spawn/, 'the prose default must stay 2');
+});