msd-core/docs/ARCHITECTURE.md

GSD Architecture

System architecture for contributors and advanced users. For user-facing documentation, see Feature Reference or User Guide.

---

Table of Contents

• System Overview
• Design Principles
• Component Architecture
• Agent Model
• Data Flow
• File System Layout
• Installer Architecture
• Hook System
• CLI Tools Layer
• Runtime Abstraction

---

System Overview

GSD is a meta-prompting framework that sits between the user and AI coding agents (Claude Code, Gemini CLI, OpenCode, Kilo, Codex, Copilot, Antigravity, Trae, Cline, Augment Code). It provides:

1. Context engineering — Structured artifacts that give the AI everything it needs per task
2. Multi-agent orchestration — Thin orchestrators that spawn specialized agents with fresh context windows
3. Spec-driven development — Requirements → research → plans → execution → verification pipeline
4. State management — Persistent project memory across sessions and context resets

┌──────────────────────────────────────────────────────┐
│                      USER                            │
│            /gsd-command [args]                        │
└─────────────────────┬────────────────────────────────┘
                      │
┌─────────────────────▼────────────────────────────────┐
│              COMMAND LAYER                            │
│   commands/gsd/*.md — Prompt-based command files      │
│   (Claude Code custom commands / Codex skills)        │
└─────────────────────┬────────────────────────────────┘
                      │
┌─────────────────────▼────────────────────────────────┐
│              WORKFLOW LAYER                           │
│   get-shit-done/workflows/*.md — Orchestration logic  │
│   (Reads references, spawns agents, manages state)    │
└──────┬──────────────┬─────────────────┬──────────────┘
       │              │                 │
┌──────▼──────┐ ┌─────▼─────┐ ┌────────▼───────┐
│  AGENT      │ │  AGENT    │ │  AGENT         │
│  (fresh     │ │  (fresh   │ │  (fresh        │
│   context)  │ │   context)│ │   context)     │
└──────┬──────┘ └─────┬─────┘ └────────┬───────┘
       │              │                 │
┌──────▼──────────────▼─────────────────▼──────────────┐
│              CLI TOOLS LAYER                          │
│   gsd-sdk query (sdk/src/query) + gsd-tools.cjs       │
│   (State, config, phase, roadmap, verify, templates)  │
└──────────────────────┬───────────────────────────────┘
                       │
┌──────────────────────▼───────────────────────────────┐
│              FILE SYSTEM (.planning/)                 │
│   PROJECT.md | REQUIREMENTS.md | ROADMAP.md          │
│   STATE.md | config.json | phases/ | research/       │
└──────────────────────────────────────────────────────┘

---

Design Principles

1. Fresh Context Per Agent

Every agent spawned by an orchestrator gets a clean context window (up to 200K tokens). This eliminates context rot — the quality degradation that happens as an AI fills its context window with accumulated conversation.

2. Thin Orchestrators

Workflow files (get-shit-done/workflows/*.md) never do heavy lifting. They:

• Load context via gsd-sdk query init.<workflow> (or legacy gsd-tools.cjs init <workflow>)
• Spawn specialized agents with focused prompts
• Collect results and route to the next step
• Update state between steps

3. File-Based State

All state lives in .planning/ as human-readable Markdown and JSON. No database, no server, no external dependencies. This means:

• State survives context resets (/clear)
• State is inspectable by both humans and agents
• State can be committed to git for team visibility

4. Absent = Enabled

Workflow feature flags follow the absent = enabled pattern. If a key is missing from config.json, it defaults to true. Users explicitly disable features; they don't need to enable defaults.

5. Defense in Depth

Multiple layers prevent common failure modes:

• Plans are verified before execution (plan-checker agent)
• Execution produces atomic commits per task
• Post-execution verification checks against phase goals
• UAT provides human verification as final gate

---

Component Architecture

Commands (commands/gsd/*.md)

User-facing entry points. Each file contains YAML frontmatter (name, description, allowed-tools) and a prompt body that bootstraps the workflow. Commands are installed as:

• Claude Code: Custom slash commands (hyphen form, /gsd-command-name)
• OpenCode / Kilo: Slash commands (hyphen form, /gsd-command-name)
• Codex: Skills ($gsd-command-name)
• Copilot: Slash commands (hyphen form, /gsd-command-name)
• Gemini CLI: Slash commands under the gsd: namespace (colon form, /gsd:command-name) — Gemini namespaces all custom commands under their plugin id, so the install path rewrites every body-text reference to colon form
• Antigravity: Skills

Total commands: see docs/INVENTORY.md for the authoritative count and full roster.

Two-stage hierarchical routing (v1.40, #2792)

To keep the eager skill-listing token cost low, v1.40 introduces six namespace meta-skills (gsd-workflow, gsd-project, gsd-review, gsd-context, gsd-manage, gsd-ideate — sourced from commands/gsd/ns-*.md, but the invocable name: is the bare form shown here) layered above the concrete sub-skills. The model sees 6 namespace routers (~120 tokens) instead of a flat 86-skill listing (~2,150 tokens), selects a namespace, then routes to the concrete sub-skill via a routing table embedded in the namespace router's body. Namespace skills are additive — every concrete command is still directly invocable.

The router descriptions use pipe-separated keyword tags (≤ 60 chars) per the Tool Attention research showing keyword-dense tags outperform prose for routing at ~40 % the token cost.

MCP token-budget interaction

The eager skill listing is one of two recurring per-turn token costs. The other is the MCP tool schema injected by every enabled MCP server in .claude/settings.json. Heavyweight MCP servers (browser/playwright, Mac-tools, Windows-tools) can each cost 20 k+ tokens per turn — often dwarfing what model_profile tuning saves. The toggle lives in the Claude Code harness (enabledMcpjsonServers / disabledMcpjsonServers in .claude/settings.json) and is not a GSD concern. Together, the two-stage routing layer (#2792) and disciplined MCP enablement are the largest cost levers per turn. See docs/USER-GUIDE.md and references/context-budget.md for the audit checklist.

Workflows (get-shit-done/workflows/*.md)

Orchestration logic that commands reference. Contains the step-by-step process including:

• Context loading via gsd-sdk query init handlers (or legacy gsd-tools.cjs init)
• Agent spawn instructions with model resolution
• Gate/checkpoint definitions
• State update patterns
• Error handling and recovery

Total workflows: see docs/INVENTORY.md for the authoritative count and full roster.

Progressive disclosure for workflows

Workflow files are loaded verbatim into Claude's context every time the corresponding /gsd-* command is invoked. To keep that cost bounded, the workflow size budget enforced by tests/workflow-size-budget.test.cjs mirrors the agent budget from #2361:

Tier	Per-file line limit
XL	1700 — top-level orchestrators (execute-phase, plan-phase, new-project)
LARGE	1500 — multi-step planners and large feature workflows
DEFAULT	1000 — focused single-purpose workflows (the target tier)

workflows/discuss-phase.md is held to a stricter <500-line ceiling per issue #2551. When a workflow grows beyond its tier, extract per-mode bodies into workflows/<workflow>/modes/<mode>.md, templates into workflows/<workflow>/templates/, and shared knowledge into get-shit-done/references/. The parent file becomes a thin dispatcher that Reads only the mode and template files needed for the current invocation.

workflows/discuss-phase/ is the canonical example of this pattern — parent dispatches, modes/ holds per-flag behavior (power.md, all.md, auto.md, chain.md, text.md, batch.md, analyze.md, default.md, advisor.md), and templates/ holds CONTEXT.md, DISCUSSION-LOG.md, and checkpoint.json schemas that are read only when the corresponding output file is being written.

Agents (agents/*.md)

Specialized agent definitions with frontmatter specifying:

• name — Agent identifier
• description — Role and purpose
• tools — Allowed tool access (Read, Write, Edit, Bash, Grep, Glob, WebSearch, etc.)
• color — Terminal output color for visual distinction

Total agents: 33

References (get-shit-done/references/*.md)

Shared knowledge documents that workflows and agents @-reference (see docs/INVENTORY.md for the authoritative count and full roster):

Core references:

• checkpoints.md — Checkpoint type definitions and interaction patterns
• gates.md — 4 canonical gate types (Confirm, Quality, Safety, Transition) wired into plan-checker and verifier
• model-profiles.md — Per-agent model tier assignments
• model-profile-resolution.md — Model resolution algorithm documentation
• verification-patterns.md — How to verify different artifact types
• verification-overrides.md — Per-artifact verification override rules
• planning-config.md — Full config schema and behavior
• git-integration.md — Git commit, branching, and history patterns
• git-planning-commit.md — Planning directory commit conventions
• questioning.md — Dream extraction philosophy for project initialization
• tdd.md — Test-driven development integration patterns
• ui-brand.md — Visual output formatting patterns
• common-bug-patterns.md — Common bug patterns for code review and verification

Workflow references:

• agent-contracts.md — Formal interface between orchestrators and agents
• context-budget.md — Context window budget allocation rules
• continuation-format.md — Session continuation/resume format
• domain-probes.md — Domain-specific probing questions for discuss-phase
• gate-prompts.md — Gate/checkpoint prompt templates
• revision-loop.md — Plan revision iteration patterns
• universal-anti-patterns.md — Common anti-patterns to detect and avoid
• artifact-types.md — Planning artifact type definitions
• phase-argument-parsing.md — Phase argument parsing conventions
• decimal-phase-calculation.md — Decimal sub-phase numbering rules
• workstream-flag.md — Workstream active pointer conventions
• user-profiling.md — User behavioral profiling methodology
• thinking-partner.md — Conditional thinking partner activation at decision points

Thinking model references:

References for integrating thinking-class models (o3, o4-mini, Gemini 2.5 Pro) into GSD workflows:

• thinking-models-debug.md — Thinking model patterns for debugging workflows
• thinking-models-execution.md — Thinking model patterns for execution agents
• thinking-models-planning.md — Thinking model patterns for planning agents
• thinking-models-research.md — Thinking model patterns for research agents
• thinking-models-verification.md — Thinking model patterns for verification agents

Modular planner decomposition:

The planner agent (agents/gsd-planner.md) was decomposed from a single monolithic file into a core agent plus reference modules to stay under the 50K character limit imposed by some runtimes:

• planner-gap-closure.md — Gap closure mode behavior (reads VERIFICATION.md, targeted replanning)
• planner-reviews.md — Cross-AI review integration (reads REVIEWS.md from /gsd-review)
• planner-revision.md — Plan revision patterns for iterative refinement

Templates (get-shit-done/templates/)

Markdown templates for all planning artifacts. Used by gsd-sdk query template.fill / phase.scaffold (and legacy gsd-tools.cjs template fill / top-level scaffold) to create pre-structured files:

• project.md, requirements.md, roadmap.md, state.md — Core project files
• phase-prompt.md — Phase execution prompt template
• summary.md (+ summary-minimal.md, summary-standard.md, summary-complex.md) — Granularity-aware summary templates
• DEBUG.md — Debug session tracking template
• UI-SPEC.md, UAT.md, VALIDATION.md — Specialized verification templates
• discussion-log.md — Discussion audit trail template
• codebase/ — Brownfield mapping templates (stack, architecture, conventions, concerns, structure, testing, integrations)
• research-project/ — Research output templates (SUMMARY, STACK, FEATURES, ARCHITECTURE, PITFALLS)

Hooks (hooks/)

Runtime hooks that integrate with the host AI agent:

Hook	Event	Purpose
gsd-statusline.js	statusLine	Displays model, task, directory, and context usage bar
gsd-context-monitor.js	PostToolUse / AfterTool	Injects agent-facing context warnings at 35%/25% remaining
gsd-check-update.js	SessionStart	Foreground trigger for the background update check
gsd-check-update-worker.js	(helper)	Background worker spawned by gsd-check-update.js; no direct event registration
gsd-prompt-guard.js	PreToolUse	Scans .planning/ writes for prompt injection patterns (advisory)
gsd-read-injection-scanner.js	PostToolUse	Scans Read tool output for injected instructions in untrusted content
gsd-workflow-guard.js	PreToolUse	Detects file edits outside GSD workflow context (advisory, opt-in via hooks.workflow_guard)
gsd-read-guard.js	PreToolUse	Advisory guard preventing Edit/Write on files not yet read in the session
gsd-session-state.sh	PostToolUse	Session state tracking for shell-based runtimes
gsd-validate-commit.sh	PostToolUse	Commit validation for conventional commit enforcement
gsd-phase-boundary.sh	PostToolUse	Phase boundary detection for workflow transitions

See docs/INVENTORY.md for the authoritative 11-hook roster.

CLI Tools (get-shit-done/bin/)

Node.js CLI utility (gsd-tools.cjs) with domain modules split across get-shit-done/bin/lib/ (see docs/INVENTORY.md for the authoritative roster):

Module	Responsibility
core.cjs	Error handling, output formatting, shared utilities; compatibility re-exports for planning helpers
planning-workspace.cjs	Planning seam (planningDir, planningPaths, active workstream routing, .planning/.lock)
state.cjs	STATE.md parsing, updating, progression, metrics
phase.cjs	Phase directory operations, decimal numbering, plan indexing
roadmap.cjs	ROADMAP.md parsing, phase extraction, plan progress
config.cjs	config.json read/write, section initialization
verify.cjs	Plan structure, phase completeness, reference, commit validation
template.cjs	Template selection and filling with variable substitution
frontmatter.cjs	YAML frontmatter CRUD operations
init.cjs	Compound context loading for each workflow type
milestone.cjs	Milestone archival, requirements marking
commands.cjs	Misc commands (slug, timestamp, todos, scaffolding, stats)
model-profiles.cjs	Model profile resolution table
security.cjs	Path traversal prevention, prompt injection detection, safe JSON parsing, shell argument validation
uat.cjs	UAT file parsing, verification debt tracking, audit-uat support
docs.cjs	Docs-update workflow init, Markdown scanning, monorepo detection
workstream.cjs	Workstream CRUD, migration, session-scoped active pointer
schema-detect.cjs	Schema-drift detection for ORM patterns (Prisma, Drizzle, etc.)
profile-pipeline.cjs	User behavioral profiling data pipeline, session file scanning
profile-output.cjs	Profile rendering, USER-PROFILE.md and dev-preferences.md generation

---

Agent Model

Orchestrator → Agent Pattern

Orchestrator (workflow .md)
    │
    ├── Load context: gsd-sdk query init.<workflow> <phase> (or legacy gsd-tools.cjs init)
    │   Returns JSON with: project info, config, state, phase details
    │
    ├── Resolve model: gsd-sdk query resolve-model <agent-name>
    │   Returns: opus | sonnet | haiku | inherit
    │
    ├── Spawn Agent (Task/SubAgent call)
    │   ├── Agent prompt (agents/*.md)
    │   ├── Context payload (init JSON)
    │   ├── Model assignment
    │   └── Tool permissions
    │
    ├── Collect result
    │
    └── Update state: gsd-sdk query state.update / state.patch / state.advance-plan (or legacy gsd-tools.cjs)

Primary Agent Spawn Categories

Conceptual spawn-pattern taxonomy for the 21 primary agents. For the authoritative 31-agent roster (including the 10 advanced/specialized agents such as gsd-pattern-mapper, gsd-code-reviewer, gsd-code-fixer, gsd-ai-researcher, gsd-domain-researcher, gsd-eval-planner, gsd-eval-auditor, gsd-framework-selector, gsd-debug-session-manager, gsd-intel-updater), see docs/INVENTORY.md.

Category	Agents	Parallelism
Researchers	gsd-project-researcher, gsd-phase-researcher, gsd-ui-researcher, gsd-advisor-researcher	4 parallel (stack, features, architecture, pitfalls); advisor spawns during discuss-phase
Synthesizers	gsd-research-synthesizer	Sequential (after researchers complete)
Planners	gsd-planner, gsd-roadmapper	Sequential
Checkers	gsd-plan-checker, gsd-integration-checker, gsd-ui-checker, gsd-nyquist-auditor	Sequential (verification loop, max 3 iterations)
Executors	gsd-executor	Parallel within waves, sequential across waves
Verifiers	gsd-verifier	Sequential (after all executors complete)
Mappers	gsd-codebase-mapper	4 parallel (tech, arch, quality, concerns)
Debuggers	gsd-debugger	Sequential (interactive)
Auditors	gsd-ui-auditor, gsd-security-auditor	Sequential
Doc Writers	gsd-doc-writer, gsd-doc-verifier	Sequential (writer then verifier)
Profilers	gsd-user-profiler	Sequential
Analyzers	gsd-assumptions-analyzer	Sequential (during discuss-phase)

Wave Execution Model

During execute-phase, plans are grouped into dependency waves:

Wave Analysis:
  Plan 01 (no deps)      ─┐
  Plan 02 (no deps)      ─┤── Wave 1 (parallel)
  Plan 03 (depends: 01)  ─┤── Wave 2 (waits for Wave 1)
  Plan 04 (depends: 02)  ─┘
  Plan 05 (depends: 03,04) ── Wave 3 (waits for Wave 2)

Each executor gets:

• Fresh 200K context window (or up to 1M for models that support it)
• The specific PLAN.md to execute
• Project context (PROJECT.md, STATE.md)
• Phase context (CONTEXT.md, RESEARCH.md if available)

Adaptive Context Enrichment (1M Models)

When the context window is 500K+ tokens (1M-class models like Opus 4.6, Sonnet 4.6), subagent prompts are automatically enriched with additional context that would not fit in standard 200K windows:

• Executor agents receive prior wave SUMMARY.md files and the phase CONTEXT.md/RESEARCH.md, enabling cross-plan awareness within a phase
• Verifier agents receive all PLAN.md, SUMMARY.md, CONTEXT.md files plus REQUIREMENTS.md, enabling history-aware verification

The orchestrator reads context_window from config (gsd-sdk query config-get context_window, or legacy gsd-tools.cjs config-get) and conditionally includes richer context when the value is >= 500,000. For standard 200K windows, prompts use truncated versions with cache-friendly ordering to maximize context efficiency.

Parallel Commit Safety

When multiple executors run within the same wave, two mechanisms prevent conflicts:

1. --no-verify commits — Parallel agents skip pre-commit hooks (which can cause build lock contention, e.g., cargo lock fights in Rust projects). The orchestrator runs git hook run pre-commit once after each wave completes.
2. STATE.md file locking — All writeStateMd() calls use lockfile-based mutual exclusion (STATE.md.lock with O_EXCL atomic creation). This prevents the read-modify-write race condition where two agents read STATE.md, modify different fields, and the last writer overwrites the other's changes. Includes stale lock detection (10s timeout) and spin-wait with jitter.

---

Data Flow

New Project Flow

User input (idea description)
    │
    ▼
Questions (questioning.md philosophy)
    │
    ▼
4x Project Researchers (parallel)
    ├── Stack → STACK.md
    ├── Features → FEATURES.md
    ├── Architecture → ARCHITECTURE.md
    └── Pitfalls → PITFALLS.md
    │
    ▼
Research Synthesizer → SUMMARY.md
    │
    ▼
Requirements extraction → REQUIREMENTS.md
    │
    ▼
Roadmapper → ROADMAP.md
    │
    ▼
User approval → STATE.md initialized

Phase Execution Flow

discuss-phase → CONTEXT.md (user preferences)
    │
    ▼
ui-phase → UI-SPEC.md (design contract, optional)
    │
    ▼
plan-phase
    ├── Research gate (blocks if RESEARCH.md has unresolved open questions)
    ├── Phase Researcher → RESEARCH.md
    ├── Planner (with reachability check) → PLAN.md files
    ├── Plan Checker → Verify loop (max 3x)
    ├── Requirements coverage gate (REQ-IDs → plans)
    └── Decision coverage gate (CONTEXT.md `<decisions>` → plans, BLOCKING — #2492)
    │
    ▼
state planned-phase → STATE.md (Planned/Ready to execute)
    │
    ▼
execute-phase (context reduction: truncated prompts, cache-friendly ordering)
    ├── Wave analysis (dependency grouping)
    ├── Executor per plan → code + atomic commits
    ├── SUMMARY.md per plan
    └── Verifier → VERIFICATION.md
        └── Decision coverage gate (CONTEXT.md decisions → shipped artifacts, NON-BLOCKING — #2492)
    │
    ▼
verify-work → UAT.md (user acceptance testing)
    │
    ▼
ui-review → UI-REVIEW.md (visual audit, optional)

Context Propagation

Each workflow stage produces artifacts that feed into subsequent stages:

PROJECT.md ────────────────────────────────────────────► All agents
REQUIREMENTS.md ───────────────────────────────────────► Planner, Verifier, Auditor
ROADMAP.md ────────────────────────────────────────────► Orchestrators
STATE.md ──────────────────────────────────────────────► All agents (decisions, blockers)
CONTEXT.md (per phase) ────────────────────────────────► Researcher, Planner, Executor
RESEARCH.md (per phase) ───────────────────────────────► Planner, Plan Checker
PLAN.md (per plan) ────────────────────────────────────► Executor, Plan Checker
SUMMARY.md (per plan) ─────────────────────────────────► Verifier, State tracking
UI-SPEC.md (per phase) ────────────────────────────────► Executor, UI Auditor

---

File System Layout

Installation Files

~/.claude/                          # Claude Code (global install)
├── commands/gsd/*.md               # Slash commands (authoritative roster: docs/INVENTORY.md)
├── get-shit-done/
│   ├── bin/gsd-tools.cjs           # CLI utility
│   ├── bin/lib/*.cjs               # Domain modules (authoritative roster: docs/INVENTORY.md)
│   ├── workflows/*.md              # Workflow definitions (authoritative roster: docs/INVENTORY.md)
│   ├── references/*.md             # Shared reference docs (authoritative roster: docs/INVENTORY.md)
│   └── templates/                  # Planning artifact templates
├── agents/*.md                     # Agent definitions (authoritative roster: docs/INVENTORY.md)
├── hooks/*.js                      # Node.js hooks (statusline, guards, monitors, update check)
├── hooks/*.sh                      # Shell hooks (session state, commit validation, phase boundary)
├── settings.json                   # Hook registrations
└── VERSION                         # Installed version number

Equivalent paths for other runtimes:

• OpenCode: ~/.config/opencode/ or ~/.opencode/
• Kilo: ~/.config/kilo/ or ~/.kilo/
• Gemini CLI: ~/.gemini/
• Codex: ~/.codex/ (uses skills instead of commands)
• Copilot: ~/.github/
• Antigravity: ~/.gemini/antigravity/ (global) or ./.agent/ (local)

Project Files (.planning/)

.planning/
├── PROJECT.md              # Project vision, constraints, decisions, evolution rules
├── REQUIREMENTS.md         # Scoped requirements (v1/v2/out-of-scope)
├── ROADMAP.md              # Phase breakdown with status tracking
├── STATE.md                # Living memory: position, decisions, blockers, metrics
├── config.json             # Workflow configuration
├── MILESTONES.md           # Completed milestone archive
├── research/               # Domain research from /gsd-new-project
│   ├── SUMMARY.md
│   ├── STACK.md
│   ├── FEATURES.md
│   ├── ARCHITECTURE.md
│   └── PITFALLS.md
├── codebase/               # Brownfield mapping (from /gsd-map-codebase)
│   ├── STACK.md            # YAML frontmatter carries `last_mapped_commit`
│   ├── ARCHITECTURE.md     # for the post-execute drift gate (#2003)
│   ├── CONVENTIONS.md
│   ├── CONCERNS.md
│   ├── STRUCTURE.md
│   ├── TESTING.md
│   └── INTEGRATIONS.md
├── phases/
│   └── XX-phase-name/
│       ├── XX-CONTEXT.md       # User preferences (from discuss-phase)
│       ├── XX-RESEARCH.md      # Ecosystem research (from plan-phase)
│       ├── XX-YY-PLAN.md       # Execution plans
│       ├── XX-YY-SUMMARY.md    # Execution outcomes
│       ├── XX-VERIFICATION.md  # Post-execution verification
│       ├── XX-VALIDATION.md    # Nyquist test coverage mapping
│       ├── XX-UI-SPEC.md       # UI design contract (from ui-phase)
│       ├── XX-UI-REVIEW.md     # Visual audit scores (from ui-review)
│       └── XX-UAT.md           # User acceptance test results
├── quick/                  # Quick task tracking
│   └── YYMMDD-xxx-slug/
│       ├── PLAN.md
│       └── SUMMARY.md
├── todos/
│   ├── pending/            # Captured ideas
│   └── done/               # Completed todos
├── threads/               # Persistent context threads (from /gsd-thread)
├── seeds/                 # Forward-looking ideas (from /gsd-plant-seed)
├── debug/                  # Active debug sessions
│   ├── *.md                # Active sessions
│   ├── resolved/           # Archived sessions
│   └── knowledge-base.md   # Persistent debug learnings
├── ui-reviews/             # Screenshots from /gsd-ui-review (gitignored)
└── continue-here.md        # Context handoff (from pause-work)

Post-Execute Codebase Drift Gate (#2003)

After the last wave of /gsd-execute-phase commits, the workflow runs a non-blocking codebase_drift_gate step (between schema_drift_gate and verify_phase_goal). It compares the diff last_mapped_commit..HEAD against .planning/codebase/STRUCTURE.md and counts four kinds of structural elements:

1. New directories outside mapped paths
2. New barrel exports at (packages|apps)/<name>/src/index.*
3. New migration files
4. New route modules under routes/ or api/

If the count meets workflow.drift_threshold (default 3), the gate either warns (default) with the suggested /gsd-map-codebase --paths … command, or auto-remaps (workflow.drift_action = auto-remap) by spawning gsd-codebase-mapper scoped to the affected paths. Any error in detection or remap is logged and the phase continues — drift detection cannot fail verification.

last_mapped_commit lives in YAML frontmatter at the top of each .planning/codebase/*.md file; bin/lib/drift.cjs provides readMappedCommit and writeMappedCommit round-trip helpers.

---

Installer Architecture

The installer (bin/install.js, ~3,000 lines) handles:

1. Runtime detection — Interactive prompt or CLI flags (--claude, --opencode, --gemini, --kilo, --codex, --copilot, --antigravity, --cursor, --windsurf, --trae, --cline, --augment, --all)
2. Location selection — Global (--global) or local (--local)
3. File deployment — Copies commands, workflows, references, templates, agents, hooks
4. Runtime adaptation — Transforms file content per runtime:

• Claude Code: Uses as-is
• OpenCode: Converts commands/agents to OpenCode-compatible flat command + subagent format
• Kilo: Reuses the OpenCode conversion pipeline with Kilo config paths
• Codex: Generates TOML config + skills from commands
• Copilot: Maps tool names (Read→read, Bash→execute, etc.)
• Gemini: Adjusts hook event names (AfterTool instead of PostToolUse)
• Antigravity: Skills-first with Google model equivalents
• Trae: Skills-first install to ~/.trae / ./.trae with no settings.json or hook integration
• Cline: Writes .clinerules for rule-based integration
• Augment Code: Skills-first with full skill conversion and config management

5. Path normalization — Replaces ~/.claude/ paths with runtime-specific paths
6. Settings integration — Registers hooks in runtime's settings.json
7. Patch backup — Since v1.17, backs up locally modified files to gsd-local-patches/ for /gsd-update --reapply
8. Manifest tracking — Writes gsd-file-manifest.json for clean uninstall
9. Uninstall mode — --uninstall removes all GSD files, hooks, and settings

Platform Handling

• Windows: windowsHide on child processes, EPERM/EACCES protection on protected directories, path separator normalization
• WSL: Detects Windows Node.js running on WSL and warns about path mismatches
• Docker/CI: Supports CLAUDE_CONFIG_DIR env var for custom config directory locations

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Hook System

Architecture

Runtime Engine (Claude Code / Gemini CLI)
    │
    ├── statusLine event ──► gsd-statusline.js
    │   Reads: stdin (session JSON)
    │   Writes: stdout (formatted status), /tmp/claude-ctx-{session}.json (bridge)
    │
    ├── PostToolUse/AfterTool event ──► gsd-context-monitor.js
    │   Reads: stdin (tool event JSON), /tmp/claude-ctx-{session}.json (bridge)
    │   Writes: stdout (hookSpecificOutput with additionalContext warning)
    │
    └── SessionStart event ──► gsd-check-update.js
        Reads: VERSION file
        Writes: ~/.claude/cache/gsd-update-check.json (spawns background process)

Context Monitor Thresholds

Remaining Context	Level	Agent Behavior
> 35%	Normal	No warning injected
≤ 35%	WARNING	"Avoid starting new complex work"
≤ 25%	CRITICAL	"Context nearly exhausted, inform user"

Debounce: 5 tool uses between repeated warnings. Severity escalation (WARNING→CRITICAL) bypasses debounce.

Safety Properties

• All hooks wrap in try/catch, exit silently on error
• stdin timeout guard (3s) prevents hanging on pipe issues
• Stale metrics (>60s old) are ignored
• Missing bridge files handled gracefully (subagents, fresh sessions)
• Context monitor is advisory — never issues imperative commands that override user preferences

Security Hooks (v1.27)

Prompt Guard (gsd-prompt-guard.js):

• Triggers on Write/Edit to .planning/ files
• Scans content for prompt injection patterns (role override, instruction bypass, system tag injection)
• Advisory-only — logs detection, does not block
• Patterns are inlined (subset of security.cjs) for hook independence

Workflow Guard (gsd-workflow-guard.js):

• Triggers on Write/Edit to non-.planning/ files
• Detects edits outside GSD workflow context (no active /gsd- command or Task subagent)
• Advises using /gsd-quick or /gsd-fast for state-tracked changes
• Opt-in via hooks.workflow_guard: true (default: false)

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Runtime Abstraction

GSD supports multiple AI coding runtimes through a unified command/workflow architecture:

Runtime	Command Format	Agent System	Config Location
Claude Code	/gsd-command	Task spawning	~/.claude/
OpenCode	/gsd-command	Subagent mode	~/.config/opencode/
Kilo	/gsd-command	Subagent mode	~/.config/kilo/
Gemini CLI	/gsd-command	Task spawning	~/.gemini/
Codex	$gsd-command	Skills	~/.codex/
Copilot	/gsd-command	Agent delegation	~/.github/
Antigravity	Skills	Skills	~/.gemini/antigravity/
Trae	Skills	Skills	~/.trae/
Cline	Rules	Rules	.clinerules
Augment Code	Skills	Skills	Augment config

Abstraction Points

1. Tool name mapping — Each runtime has its own tool names (e.g., Claude's Bash → Copilot's execute)
2. Hook event names — Claude uses PostToolUse, Gemini uses AfterTool
3. Agent frontmatter — Each runtime has its own agent definition format
4. Path conventions — Each runtime stores config in different directories
5. Model references — inherit profile lets GSD defer to runtime's model selection

The installer handles all translation at install time. Workflows and agents are written in Claude Code's native format and transformed during deployment.