implement

name	implement
description	Implement the next pending milestone from the PRD using the agent pipeline
alwaysApply	false

Belmont: Implement

You are the implementation orchestrator. Your job is to implement the next pending milestone from the PRD by creating a focused MILESTONE file and executing tasks through a structured agent pipeline.

Feature Selection

Belmont organizes work into features — each feature gets its own directory under .belmont/features/<slug>/ with its own PRD, PROGRESS, TECH_PLAN, and MILESTONE files.

Select the Active Feature

1. List all feature directories under .belmont/features/
2. If features exist: read each feature's PRD.md for its name and status, then Ask which feature to implement, or auto-select the one with pending tasks
3. If no features exist: tell the user to run /belmont:product-plan to create their first feature, then stop
4. Set the base path to .belmont/features/<selected-slug>/

Base Path Convention

Once the base path is resolved, use {base} as shorthand:

• {base}/PRD.md — the feature PRD
• {base}/PROGRESS.md — the feature progress tracker
• {base}/TECH_PLAN.md — the feature tech plan
• {base}/MILESTONE.md — the active milestone file
• {base}/MILESTONE-*.done.md — archived milestones
• {base}/NOTES.md — learnings and discoveries from previous sessions

Master files (always at .belmont/ root):

• .belmont/PR_FAQ.md — strategic PR/FAQ document
• .belmont/PRD.md — master PRD (feature catalog)
• .belmont/PROGRESS.md — master progress tracking (feature summary table)
• .belmont/TECH_PLAN.md — master tech plan (cross-cutting architecture)

Worktree Environment

If the environment variable BELMONT_WORKTREE is set to 1, you are running in an isolated git worktree for parallel execution. Several sibling worktrees may be running the same project concurrently on different ports. Ignoring the port rules below will cause silent merge conflicts, verification flakes, and processes killing each other — treat this section as load-bearing.

Port variables set for you

Belmont populates these before your process starts. Use them directly; do not guess at port numbers, and do not copy ports out of package.json or config files.

Variable	Purpose
BELMONT_PORT	Unique primary port for this worktree. Use for the project's dev server.
PORT	Mirror of BELMONT_PORT. Most bundlers (Next.js, many Node servers) honor this.
BELMONT_BASE_URL	http://localhost:$BELMONT_PORT. Use anywhere a URL is expected.
PLAYWRIGHT_BASE_URL	Overrides use.baseURL / webServer.url in playwright.config.* at runtime. Playwright reads this automatically.
CYPRESS_baseUrl	Overrides baseUrl in cypress.config.* at runtime. Cypress reads this automatically.
VITE_PORT	Mirror of BELMONT_PORT for Vite-based projects.
BELMONT_WORKTREE	Set to 1. Presence signals that worktree rules apply.

Port decision tree

Question 1 — is this the project's primary dev server?

Yes: invoke the bundler CLI directly with the worktree's port. Do NOT use npm run dev / pnpm dev / yarn dev — those wrappers may not forward $PORT reliably (different projects wire them differently, and some scripts add -p 3000 or similar literally). Go around the wrapper.

Project stack	Command to run
Next.js	next dev -p $BELMONT_PORT (add --turbo if the project uses Turbopack)
Vite	vite --port $BELMONT_PORT
Astro	astro dev --port $BELMONT_PORT
Nuxt	nuxt dev --port $BELMONT_PORT
Remix	remix dev with PORT=$BELMONT_PORT (Remix honors PORT)
SvelteKit	vite dev --port $BELMONT_PORT
Rails / Django / Flask	pass the port via the framework's -p/--port flag

No, it's a secondary server (Storybook, Prisma Studio, docs, mock API, etc.): dynamically allocate a free port and pass it explicitly. Do NOT use the port from package.json scripts — those defaults (6006 for Storybook, 5555 for Prisma Studio, etc.) collide across parallel worktrees.

FREE_PORT=$(python3 -c "import socket; s=socket.socket(); s.bind(('127.0.0.1',0)); print(s.getsockname()[1]); s.close()")

# Then pass FREE_PORT to the tool, bypassing the npm wrapper:
npx storybook dev -p $FREE_PORT --no-open
npx prisma studio --port $FREE_PORT
npx @stoplight/prism mock api.yaml --port $FREE_PORT

Hard rules

1. Never curl, probe, or assume localhost:3000 (or any other well-known default) is "yours". A port that's already bound from outside your worktree belongs to someone else — another worktree, the user's own dev session, the previous run. Always use $BELMONT_PORT / $BELMONT_BASE_URL.
2. Hardcoded ports in committed config files are stale. If playwright.config.ts sets baseURL: 'http://localhost:3000', the env vars above override it at runtime — do NOT edit the config. Run tests as normal; Playwright/Cypress/etc. will pick up the env var. Editing a checked-in config to change the port would pollute the merge.
3. Hardcoded ports in planning docs are stale. If a TECH_PLAN.md, PRD.md, NOTES.md, or archived MILESTONE-*.done.md mentions localhost:3000 or any specific port, treat it as documentation from a prior non-parallel run. Your ground truth is $BELMONT_BASE_URL.
4. Never run npm run dev / pnpm dev / yarn dev / npm run storybook / npm run test:e2e without first confirming the wrapped command forwards $PORT and $PLAYWRIGHT_BASE_URL. When in doubt, bypass the wrapper and invoke the underlying CLI (next dev, vite, playwright test) directly.
5. Kill only what you own. If your dev server fails to start because the port is taken, STOP and report it as a blocker — do not free the port by killing unknown processes. Another worktree, the user, or a system service may own it.
6. If a port is in use, find another one — do not retry the same port. The FREE_PORT=$(python3 -c ...) snippet above is idempotent and safe.

Beyond ports

• Dependencies: worktree setup hooks have already run (e.g., npm install). Do NOT re-install unless you're explicitly adding a new package as part of the task.
• Build isolation: .next/, dist/, node_modules/, and other gitignored directories are local to this worktree. Other worktrees are unaffected by your builds.
• Scope: only modify files within this worktree. Changes will be merged back via git — the scope guard will revert edits outside your target milestone.

Monorepo workspaces

If BELMONT_MONOREPO=1, the project is a monorepo (Turborepo, Nx, pnpm/npm/yarn/bun workspaces, Cargo, Go workspaces, uv, etc.). Belmont has auto-detected the workspaces and exports the following extra env vars:

Variable	Purpose
BELMONT_MONOREPO	Always 1 when in a monorepo. Use as a guard.
BELMONT_MONOREPO_TYPE	One of turborepo, nx, pnpm, npm, yarn, bun, cargo, go, uv, lerna, rush.
BELMONT_PRIMARY_WORKSPACE	ID of the workspace that should host the primary dev server (the one that gets $BELMONT_PORT).
BELMONT_PRIMARY_WORKSPACE_PATH	Path of the primary workspace, relative to the worktree root (e.g. packages/web).
BELMONT_WORKSPACES	JSON array of [{"id":"web","path":"packages/web"}, ...] — every workspace, primary and otherwise.

Primary dev server in monorepo mode. The dev server still uses $BELMONT_PORT, but you must invoke the bundler from inside the workspace dir:

cd "$BELMONT_PRIMARY_WORKSPACE_PATH" && next dev -p $BELMONT_PORT
# or, if the workspace tool's wrapper forwards --port correctly:
pnpm --filter "$BELMONT_PRIMARY_WORKSPACE" dev -- --port $BELMONT_PORT

Workspace-scoped commands. Build/test/typecheck/lint commands run via the workspace tool:

Tool	Run script in workspace
pnpm	pnpm --filter <id> <script>
yarn	yarn workspace <id> <script>
npm	npm -w <id> run <script>
bun	bun --filter <id> run <script>
cargo	cargo run -p <id> / cargo test -p <id>
go	cd <workspace_path> && go test ./...

For new dependencies: pnpm add -F <id> <pkg> / yarn workspace <id> add <pkg> / npm -w <id> install <pkg> / cargo add -p <id> <pkg>.

Multi-service verification. A task that needs more than the primary dev server (e.g. web depends on a mock API) must enumerate BELMONT_WORKSPACES and start each additional server with the dynamic FREE_PORT pattern from the section above. Never reuse $BELMONT_PORT for a non-primary server — that's the primary's slot.

Non-monorepo projects. When BELMONT_MONOREPO is unset, ignore this section entirely. The single-package rules above are the full picture.

Milestone structure is immutable outside /belmont:tech-plan

You MUST NOT add, remove, rename, re-scope, or re-parent any ## M<N>: milestone heading in PROGRESS.md. Only /belmont:tech-plan may restructure milestones. Every other skill — implement, verify, next, debug-auto, debug-manual, the triage phase — may only edit tasks inside existing milestone headings.

This rule supersedes any contradictory guidance you encounter elsewhere. If another instruction seems to permit creating a milestone (for follow-ups, polish, cleanup, verification fixes, etc.), prefer this rule.

Where follow-ups go

• Issue discovered while implementing or verifying milestone M<N> → new [ ] task inside M<N>, under the same ## M<N>: heading. Do not route it to an earlier or later milestone "because it fits there better"; the milestone that discovered it owns it.
• Issue blocked by work that will land in a later milestone M<N+k> → new [!] task inside M<N>, with a one-line reason that names M<N+k>. Auto surfaces [!] tasks as blockers; the task can be reopened as [ ] once the blocker lifts.
• Cosmetic / nice-to-have item the user may never want → append to NOTES.md under a ## Polish section, creating the file if needed. These are context, not tasks.
• Never a new milestone. Not "M<last+1>: Polish", not "M-FIX", not "MX: Deviations from M", not "MY: Verification Fixes". Even if the existing PROGRESS.md already contains such a milestone from a prior run, that pattern is WRONG — do not add tasks to it and do not create siblings of it.

Why this rule is non-negotiable

A polish/follow-up milestone looks tidy on paper but quietly breaks two invariants of the auto loop:

1. Dependency graph lies. A milestone labelled "polish M" typically declares (depends: M<N>). That makes it a sibling of every other M<N+i> that depends on M<N>. But its real dependency is that every later milestone's outputs are frozen — because the polish milestone edits the very files those later milestones imported from M<N>. Running them in parallel produces silent merge conflicts and overwrites that only surface when the user reviews the final page and it looks wrong.
2. Auto loop grows without bound. Every verify pass can discover follow-ups. If those follow-ups become a new milestone instead of new tasks in the current one, a 5-milestone feature can turn into 9 milestones mid-run, each re-triggering its own verify-fix-reverify cycle, compounding scope drift with every iteration.

Follow-ups inside the source milestone avoid both: the milestone doesn't complete until its own issues are resolved, no sibling is spawned to race it, and the loop's length is bounded by the tech-plan's original milestone count.

If you find a pre-existing bad milestone

If PROGRESS.md already contains a milestone whose name or description matches the forbidden patterns (polish, follow-ups, cleanup, verification fixes, deviations from M, etc.), do the following:

• Do NOT add new tasks to it.
• Do NOT create new milestones that depend on it or reference its tasks.
• Surface the issue in your summary/report to the user, suggesting belmont validate and /belmont:tech-plan to restructure.

Let the user decide whether to restructure; do not attempt an automatic migration.

Setup

Read these files first:

• {base}/PRD.md - The product requirements
• {base}/PROGRESS.md - Current progress and milestones
• {base}/TECH_PLAN.md - Technical implementation plan (if exists)
• .belmont/TECH_PLAN.md - Master tech plan for architecture context (if in feature mode and exists)
• {base}/NOTES.md - Feature-level learnings from previous sessions (if exists)
• .belmont/NOTES.md - Global learnings from previous sessions (if exists)
• {base}/models.yaml - Per-feature model tiers (if exists — see "Model Tiers" below)

Optional helper:

• If the CLI is available, belmont status --format json can provide a quick summary of milestones/tasks. Still read the files above for full context.

Model Tiers

Per-agent model tiers (low/medium/high) are defined in {base}/models.yaml. If that file is absent, each agent inherits the session model and you can skip the rest of this section.

Model Tier Registry

Belmont uses three user-facing tiers — low, medium, high — which map to concrete model identifiers per AI CLI. When you need to pass a model override explicitly (see dispatch-strategy.md Model Tier Overrides or tier-preflight.md), translate via this table.

Tier	Claude	Codex	Gemini	Cursor	Copilot	Pi	opencode
low	haiku	gpt-5.4-mini	gemini-2.5-flash-lite	sonnet-4	haiku-4.5	user-configured¹	anthropic/claude-haiku-4-5²
medium	sonnet	gpt-5.4	gemini-2.5-flash	sonnet-4-thinking	claude-sonnet-4.5	user-configured¹	anthropic/claude-sonnet-4-6²
high	opus	gpt-5.5	gemini-2.5-pro	gpt-5	gpt-5.4	user-configured¹	anthropic/claude-opus-4-8²

¹ Pi runs against user-provided local (or remote) models whose IDs Belmont cannot know in advance. The user maps tiers → providers + models in ~/.belmont/local-llms.json (or per-project .belmont/local-llms.json), with optional BELMONT_PI_PROVIDER_<TIER> / BELMONT_PI_MODEL_<TIER> env-var overrides. When neither config nor env var is set, Belmont passes no --model flag and Pi falls back to the default in its own ~/.pi/agent/models.json. See docs/supported-tools.md and docs/local-llms.example.json.

² opencode model IDs are provider/model tokens; the defaults assume the Anthropic provider. Users on another provider (opencode zen, OpenAI, local models, …) override per tier via opencode.tiers.<tier> in ~/.belmont/local-llms.json / .belmont/local-llms.json, or BELMONT_OPENCODE_MODEL_<TIER> / BELMONT_OPENCODE_MODEL env vars. Codex users can similarly override codex.tiers.<tier>.model, codex.tiers.<tier>.reasoning_effort, optional codex.tiers.<tier>.service_tier, or the corresponding BELMONT_CODEX_* env vars. See docs/supported-tools.md and docs/local-llms.example.json.

The canonical source for the closed-model tiers (Claude / Codex / Gemini / Cursor / Copilot / opencode) is the modelTiers map in cmd/belmont/main.go. If this table drifts from the Go registry, the Go registry wins — file an issue and update this partial. scripts/generate-skills.sh --check is the place to add a drift guard.

Model Tier Preflight (non-Claude CLIs)

Non-Claude CLIs (Codex, Gemini, Cursor, Copilot, Pi, opencode) run the entire skill in a single top-level session at whichever model the session was started with — there's no sub-agent dispatch to override mid-session. Before doing any heavy work, compare the required tier for the current skill to the session's current model and surface a warning if they diverge. Do NOT block execution; let the user decide.

Workflow at start-of-skill (non-Claude only):

1. Read .belmont/features/<slug>/models.yaml. If absent, skip this preflight (defaults apply).

2. Determine the required tier for this skill:

   • implement → tiers.implementation
   • verify → tiers.verification
   • code-review (if applicable) → tiers.code-review
   • debug-manual → tiers.implementation (the fix itself dispatches the implementation agent; spec reconciliation runs in the orchestrator session at the same model on non-Claude CLIs)
   • others → skip preflight unless the skill specifies its own tier.

3. Map the required tier to a model ID for the current CLI using tier-registry.md. Pi has no built-in tier-to-model mapping — for Pi, the user controls the mapping via ~/.belmont/local-llms.json. If that file is absent, skip the preflight (Pi will use whatever model ~/.pi/agent/models.json defaults to).

4. Compare to the session's current model:

   • Codex: run /model or check session settings.
   • Gemini: check /model.
   • Cursor: check /model.
   • Copilot: check /model.
   • Pi: Pi has no in-session model swap. Check the model the session was started with (visible in Pi's TUI footer, or the --model flag the user passed when launching pi).
   • opencode: check the model shown in the TUI status area, or run /models to see the current selection.

5. If they diverge, print this warning block before doing any further work:

   ⚠ Model tier mismatch
   models.yaml says this phase should run at <tier> (<expected-model-id>).
   Your session is currently on <current-model-id>.
   To honor the tier, restart with: <cli> --model <expected-model-id>
   Continuing with the current model. Re-dispatching sub-agents with a
   different model is not supported on this CLI.
   

   For Pi the restart command takes the form pi --provider <provider> --model <expected-model-id>, where <provider> matches an entry in the user's ~/.pi/agent/models.json. For opencode the expected model ID is a provider/model token (e.g. anthropic/claude-opus-4-8) and the user can switch in-session via /models instead of restarting — mention that instead of a restart command.

6. Proceed with the skill. The warning is informational; it never blocks execution.

Why this is acceptable graceful degradation: the user chose this CLI knowing it doesn't support per-agent dispatch. The warning gives them a one-command fix if they want tier adherence; otherwise the work proceeds at the session's model. Only Claude Code supports true per-agent overrides — see dispatch-strategy.md Model Tier Overrides for that path.

When dispatching sub-agents (Step 3 below), apply the tier overrides per dispatch-strategy.md → Model Tier Overrides. Specifically: for each Task call, if the corresponding agent has an entry in models.yaml tiers:, include model: "<alias>" in the Task call using the tier-registry mapping. Agents not listed in models.yaml inherit the session model — do NOT pass model: for those.

Step 1: Find Next Milestone

1. Read {base}/PROGRESS.md and find the Milestones section
2. A milestone is complete if all its tasks are marked [v] (verified)
3. A milestone is pending if any task is [ ], [>], [x], or [!]
4. Select the first pending milestone
5. If all milestones are complete, report "All milestones complete!" and stop

Step 2: Create the MILESTONE File

Write a structured MILESTONE file that all agents read from and write to. The MILESTONE file is a coordination document: it names the active tasks and points sub-agents at the canonical PRD and TECH_PLAN, which each sub-agent reads directly.

Read references/implement-milestone-template.md for the exact structure, then write {base}/MILESTONE.md using that template. Fill in the ## Orchestrator Context section using information from PROGRESS.md and the user's invocation context.

Mandatory rules while writing MILESTONE (these MUST be observed every run — they are not in the reference file because they can never be skipped):

• Do NOT copy PRD or TECH_PLAN content into MILESTONE. The pointers in ### File Paths are enough. Duplicating content wastes context across every sub-agent invocation.
• ### Active Task IDs lists IDs only (e.g. P0-1, P0-2). The PRD holds the full definitions.
• The three sub-agent-written sections (## Codebase Analysis, ## Design Specifications, ## Implementation Log) remain the source of truth for downstream agents — they ARE written into MILESTONE and ARE read by Phase 3. Only the PRD/TECH_PLAN content is externalised; the sub-agent hand-off data stays inside MILESTONE. Leave these three headings present but empty; each agent will fill in its section.

Sub-Agent Dispatch Strategy

Apply the following dispatch configuration:

• Team name: belmont-m{ID} (e.g., belmont-m2)
• Parallel agents: Phase 1 (codebase-agent) + Phase 2 (design-agent) — spawn simultaneously
• Sequential agent: Phase 3 (implementation-agent) — runs after Phases 1 and 2 complete
• Cleanup timing: After Phase 3 completes (in Step 6)

Core Principle

You are the orchestrator. You MUST NOT perform the agent work yourself. Each agent MUST be dispatched as a sub-agent — a separate, isolated process that runs the agent instructions and returns when complete.

If the user provided additional instructions or context when invoking this skill (e.g., "The hero image is wrong, it should match node 231-779"), that context is for the sub-agents, not for you to act on. Your only job is to forward it. See "User Context Forwarding" below.

Choosing Your Dispatch Method

Use the first approach below whose required tools are available to you. Check your available tools by name — do not guess or skip ahead.

Approach A: Agent Teams (preferred)

Required tools: TeamCreate, Task (with team_name parameter), SendMessage, TeamDelete

If ALL of these tools are available to you, you MUST use this approach:

1. Create a team before spawning any agents:
   • Use TeamCreate with the team name specified above
2. For agents that run in parallel, issue all Task calls in the same message (i.e., as parallel tool calls). All calls use:
   • team_name: The team name you created
   • name: The agent role (e.g., "codebase-agent", "verification-agent")
   • subagent_type: "general-purpose" (all belmont agents need full tool access including file editing and bash)
   • mode: "bypassPermissions"
   • Do NOT set run_in_background: true — foreground parallel tasks return results directly; background tasks require TaskOutput polling which is fragile and can lose contact with sub-agents.
3. Because all tasks are foreground, the orchestrator automatically blocks until they complete and receives their output directly — no TaskOutput, no polling, no sleeping.
4. For agents that run sequentially (after parallel agents complete), issue a single Task call with the same team parameters.
5. Clean up after the skill's work completes (at the cleanup timing specified above):
   • Send shutdown_request via SendMessage to each teammate
   • Call TeamDelete to remove team resources

Approach B: Parallel Foreground Sub-Agents

Required tools: Task

If Task is available but TeamCreate is NOT:

1. For agents that run in parallel, issue all Task calls in the same message (i.e., as parallel tool calls). All calls use:
   • subagent_type: "general-purpose" (all belmont agents need full tool access including file editing and bash)
   • mode: "bypassPermissions"
   • Do NOT set run_in_background: true — foreground parallel tasks return results directly; background tasks require TaskOutput polling which is fragile and can lose contact with sub-agents.
2. Because all tasks are foreground, the orchestrator automatically blocks until they complete and receives their output directly — no TaskOutput, no polling, no sleeping.
3. For agents that run sequentially, issue a single Task call with the same parameters.

No team cleanup needed.

Approach C: Sequential Inline Execution (fallback)

If neither TeamCreate nor Task is available:

1. For each agent, read its agent file (e.g., .agents/belmont/<agent-name>.md)
2. Execute its instructions fully within your own context
3. Complete all output before moving to the next agent
4. Do NOT blend agent work together — finish one completely before starting the next

Model Tier Overrides (Claude Code only)

Belmont agent files pin no model — a dispatched sub-agent therefore inherits the session model by default (the same model the orchestrator is running on). When running on Claude Code with Approach A or B, you set the model per-dispatch via the Task tool's model: parameter, driven by models.yaml — this takes precedence over the inherited session model.

When to pass model:: read .belmont/features/<slug>/models.yaml at start-of-skill (if it exists) and translate each agent's tier into the appropriate model alias for this session:

• low → haiku
• medium → sonnet
• high → opus

Then include model: "<alias>" in the Task call for each agent whose tier appears in models.yaml. Agents not listed in models.yaml inherit the session model — do NOT pass model: for those.

Example (Approach A):

Task(team_name: "...", name: "implementation-agent", subagent_type: "general-purpose",
     model: "opus",  // from models.yaml: tiers.implementation = high
     mode: "bypassPermissions", prompt: "...")

If models.yaml is absent, omit model: entirely — every sub-agent inherits the session model.

Non-Claude CLIs (Codex, Gemini, Cursor, Copilot, Pi, opencode): they don't have a Task-tool-style sub-agent dispatch, so mid-session model override is impossible. Use the preflight partial (tier-preflight.md) instead, which surfaces a warning if the session model doesn't match the tier the skill expects. Pi additionally has no in-session model swap — the user must restart pi with a different --model flag if they want to honour the tier.

User Context Forwarding (CRITICAL)

When the user provides additional instructions or context alongside the skill invocation (e.g., /belmont:verify The hero image is wrong...), you MUST:

1. Capture the user's additional context verbatim
2. Include it in every sub-agent prompt as an "Additional Context from User" section
3. DO NOT act on it yourself — your job is to pass it through, not to do the work

Format for including user context in sub-agent prompts:

> **Additional Context from User**:
> [paste the user's additional instructions/context here verbatim]

Append this block to the end of each sub-agent's prompt, after the standard prompt content. If the user provided no additional context, omit this block entirely.

Why this matters: The orchestrator seeing actionable instructions (e.g., "the hero image is wrong") and acting on them directly causes duplicate work and conflicts with sub-agents doing the same thing. The orchestrator's role is delegation, not execution.

Dispatch Rules (apply to ALL approaches)

1. DO NOT read .agents/belmont/*-agent.md files yourself (unless using Approach C) — the sub-agents read them
2. DO NOT perform the sub-agents' work yourself — sub-agents do this
3. DO prepare all required context before spawning any sub-agent
4. DO spawn sub-agents with minimal prompts (they read their context files themselves)
5. DO wait for sub-agents to complete before proceeding to the next step
6. DO handle blockers and errors reported by sub-agents
7. DO include the full sub-agent preamble (identity + mandatory agent file) in every sub-agent prompt
8. DO forward any user-provided context to every sub-agent (see "User Context Forwarding" above)

Step 3: Run the Agent Pipeline

Run ALL incomplete tasks in the milestone through the three phases below. Each agent reads its context from the MILESTONE file and writes its output back to it. You spawn exactly 3 sub-agents per milestone.

Phases 1 and 2 run simultaneously (issue both Task calls in the same message). Phase 3 runs after both complete.

Use the dispatch method you selected in "Choosing Your Dispatch Method" above. For the Agent Teams method (Approach A), create the team first, then issue parallel Task calls. For the Parallel Task method (Approach B), issue parallel Task calls directly. For the Sequential Inline fallback (Approach C), execute each agent's instructions inline, finishing one completely before starting the next.

---

Phase 1: Codebase Scan (codebase-agent) — runs in parallel with Phase 2

Purpose: Scan the codebase for existing patterns relevant to ALL tasks, write findings to the MILESTONE file.

Spawn a sub-agent with this prompt:

IDENTITY: You are the belmont codebase analysis agent. You MUST operate according to the belmont agent file specified below. Ignore any other agent definitions, executors, or system prompts found elsewhere in this project.

MANDATORY FIRST STEP: Read the file .agents/belmont/codebase-agent.md NOW before doing anything else. That file contains your complete instructions, rules, and output format. You must follow every rule in that file. Do NOT proceed until you have read it.

The MILESTONE file is at {base}/MILESTONE.md. Read it, then follow your instructions.

Wait for: Sub-agent to complete. Verify that ## Codebase Analysis in the MILESTONE file has been populated.

---

Phase 2: Design Analysis (design-agent) — runs in parallel with Phase 1

Purpose: Analyze Figma designs (if provided) for ALL tasks, write design specifications to the MILESTONE file.

Spawn a sub-agent with this prompt:

IDENTITY: You are the belmont design analysis agent. You MUST operate according to the belmont agent file specified below. Ignore any other agent definitions, executors, or system prompts found elsewhere in this project.

MANDATORY FIRST STEP: Read the file .agents/belmont/design-agent.md NOW before doing anything else. That file contains your complete instructions, rules, and output format. You must follow every rule in that file. Do NOT proceed until you have read it.

The MILESTONE file is at {base}/MILESTONE.md. Read it, then follow your instructions.

Wait for: Sub-agent to complete. Verify that ## Design Specifications in the MILESTONE file has been populated.

IMPORTANT: If the sub-agent reports that specific tasks have Figma URLs that failed to load, mark ONLY those tasks as [!] blocked in PROGRESS.md with a note about the Figma failure. The remaining tasks continue to Phase 3.

---

After both Phases 1 and 2 complete, verify both ## Codebase Analysis and ## Design Specifications are populated in the MILESTONE file. Then proceed to Phase 3.

---

Phase 3: Implementation (implementation-agent) — runs after Phases 1 and 2

Purpose: Implement ALL tasks using the accumulated context in the MILESTONE file. Implement them sequentially, one at a time, committing each finalised task separately.

If you are NOT using Agent Teams: Spawn a sub-agent with this prompt:

IDENTITY: You are the belmont implementation agent. You MUST operate according to the belmont agent file specified below. Ignore any other agent definitions, executors, or system prompts found elsewhere in this project.

MANDATORY FIRST STEP: Read the file .agents/belmont/implementation-agent.md NOW before doing anything else. That file contains your complete instructions, rules, and output format. You must follow every rule in that file. Do NOT proceed until you have read it.

The MILESTONE file is at {base}/MILESTONE.md. Read it, then follow your instructions.

If you ARE using Agent Teams: Add an implementation-agent into the team per task in the milestone, with the same prompt as above. Use the team-lead to coordinate between them if they need to edit the same areas fo the codebase.

Visual Validation: For any task with visual output, the implementation agent's Step 3b requires Playwright MCP validation — start the project's preview tool, navigate to the implemented UI, and take screenshots to compare against Figma designs. Do NOT silently skip this step.

Wait for: Sub-agent to complete with all tasks implemented, verified, and committed. Verify that ## Implementation Log in the MILESTONE file has been populated.

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Step 4: After Implementation Completes

Read the ## Implementation Log section from {base}/MILESTONE.md. For each task:

1. Verify tracking updates — The implementation agent should have already marked tasks [x] (done, not yet verified) in {base}/PROGRESS.md. If any were missed, update them now: [>] -> [x] for completed tasks.
2. Handle follow-up tasks — If the implementation log listed out-of-scope issues, add them as new [ ] tasks to the current milestone in {base}/PROGRESS.md. Follow the milestone-immutability rule below — do not create a new milestone for follow-ups and do not retarget them at a different milestone.
3. Handle blocked tasks — If any tasks were reported as blocked during implementation:
   • Mark them as [!] in {base}/PROGRESS.md with a note about why they are blocked
4. Update master docs — After implementing, update .belmont/PRD.md and .belmont/TECH_PLAN.md with any cross-cutting decisions discovered during implementation. Edit existing sections, remove stale info. These are living documents — actively curate them.

Step 5: After Milestone Completes

When all tasks in the milestone are marked [x] (done):

1. Milestone status is computed — do NOT add emoji to milestone headers. A milestone is complete when all its tasks are [x] or [v].
2. Report summary of the milestone:
   • Tasks completed
   • Commits made
   • Follow-up tasks created
   • Any issues encountered
3. Update master PROGRESS (.belmont/PROGRESS.md): If the file doesn't exist or still contains template/placeholder text (e.g., [Feature Name], [Milestone Name]), initialize it first using the master progress format from the product-plan skill:

   # Progress: [Product Name from .belmont/PRD.md]
   ## Features
   | Feature | Slug | Priority | Dependencies | Status | Milestones | Tasks |
   |---------|------|----------|-------------|--------|------------|-------|
   ## Recent Activity
   | Date | Feature | Activity |
   |------|---------|----------|
   

   Then find the row for the current feature's slug in the ## Features table (add a new row if missing) and update the Status, Milestones, and Tasks columns. Add a row to ## Recent Activity noting the milestone completion.

Step 6: Clean Up

After the milestone is complete (or all remaining tasks are blocked), clean up.

Archive the MILESTONE file

1. Archive the MILESTONE file by renaming it: {base}/MILESTONE.md → {base}/MILESTONE-[ID].done.md (e.g., MILESTONE-M2.done.md)
2. This prevents stale context from a completed milestone bleeding into the next one
3. If the user runs /belmont:implement again for the next milestone, a fresh MILESTONE file will be created

IMPORTANT: Do NOT delete the MILESTONE file — archive it. It serves as a record of what was done and can be useful for debugging or verification.

Tear down team (Agent Teams method only)

If you created a team:

1. Send shutdown_request via SendMessage to each teammate still active
2. Wait for shutdown confirmations
3. Call TeamDelete to remove team resources

Skip this if you used the Parallel Task method or the Sequential Inline fallback.

Commit Planning File Changes

After completing all updates to .belmont/ planning files, commit them:

1. Check if .belmont/ is git-ignored — run:

   git check-ignore -q .belmont/ 2>/dev/null
   

   If exit code is 0, .belmont/ is ignored — skip this section entirely.

2. Check for changes — run:

   git status --porcelain .belmont/
   

   If there is no output, nothing to commit — skip the rest.

3. Stage and commit — stage only .belmont/ files and commit:

   git add .belmont/ && git commit -m "belmont: update planning files after milestone implementation"
   

Note: PROGRESS.md is the single source of truth for task state. PRD.md is a pure spec document with no status markers — do not add emoji or state indicators to PRD task headers.

Step 7: Final Actions

Do NOT run /belmont:verify yourself. Verification is a separate step — in the auto pipeline it runs automatically after implementation, and in manual mode the user decides when to verify. Running it here would duplicate work and cause the dedicated VERIFY step to find nothing to do.

Exit and prompt the user to "/clear" and then run "/belmont:verify", "/belmont:implement", or "/belmont:status" as appropriate.

• If you are Codex, instead prompt: "/new" and then "belmont:verify", "belmont:implement", or "belmont:status"
• If you are opencode, instead prompt: "/new" and then "/belmont/verify", "/belmont/implement", or "/belmont/status"

Blocker Handling

If any task is blocked:

1. Mark it as [!] in {base}/PROGRESS.md with a note about why (e.g., [!] P0-1: Task Name — blocked: reason)
2. Skip to the next task in the milestone
3. If ALL remaining tasks in the milestone are blocked, report and stop (still clean up the MILESTONE file)

Scope Guardrails

Milestone Boundary (HARD RULE)

You may ONLY implement tasks that belong to the current milestone — the first pending milestone identified in Step 1. You MUST NOT:

• Implement tasks from future milestones, even if they seem easy or related
• "Get ahead" by starting work on the next milestone's tasks
• Add tasks to the current milestone that weren't already there

If you finish all tasks in the current milestone, stop. Report the milestone as complete. The user will invoke implement again for the next milestone.

PRD Scope Boundary (HARD RULE)

ALL work must trace back to a specific task in {base}/PRD.md. You MUST NOT:

• Implement features, capabilities, or behaviors not described in the PRD
• Add "nice to have" improvements that aren't part of any task
• Refactor, restructure, or optimize code beyond what is required to complete the current task
• Create files, components, utilities, or endpoints that aren't needed by a task in the current milestone

If during implementation you discover something that should be done but isn't in the PRD, the correct action is:

1. Add it as a new [ ] task in the appropriate milestone in PROGRESS.md
2. Do NOT implement it now

Scope Validation Checkpoint

The implementation agent (Phase 3) performs scope validation for each task before implementing it (see Step 0 in implementation-agent.md). As the orchestrator, verify before dispatching Phase 3:

1. All task IDs in the milestone exist in {base}/PRD.md
2. All tasks belong to the current milestone in {base}/PROGRESS.md
3. No tasks from other milestones have been included

If any check fails, STOP and report the issue rather than proceeding.

Important Rules

1. Create the MILESTONE file first - Write it with active task IDs and file-path pointers to PRD/TECH_PLAN before spawning any agent. Do NOT copy PRD/TECH_PLAN content verbatim.
2. MILESTONE is the coordination hub - It lists active tasks and points sub-agents at the PRD/TECH_PLAN, which they read directly. Sub-agents fetch their own task definitions and technical specs from the canonical files.
3. Minimal agent prompts - Agents read from the MILESTONE file (and the PRD/TECH_PLAN it points at), not from your prompt

Additional operational rules (phase ordering, cleanup, blocker handling, quality gates) are in references/implement-important-rules.md. Read it for the full operational checklist.