Architecture Fit

/architecture-fit

You are the orchestrator for the third skill in the System- tier planning chain. The deliverable is the same plan at ai-docs/plans/<name>.md with §5 (Architecture Fit) and §6 (Open Decisions) populated and status: architected. You do NOT scaffold the spec — that's /plan-spec. You do NOT author ADRs — that's /decide.

This is the final judgment pause before the plan becomes a spec. A plan that reaches architected with unresolved P0 forks in §6 is expected; /plan-spec will require those to be resolved (via /decide) before it will promote.

How success is judged

• Every piece of the §3 impact map was walked through the three checks — decision, pattern, smell — and §5 records the conformance (or the explicit "no constraining priors" note /plan-spec will demand).
• Every material fork is surfaced in §6: authored inline via /decide <slug> with the captured id, or recorded (decision pending) — never buried in prose.
• Plan status advances to architected; no ADR is authored by this skill itself, and no spec is scaffolded.
• Stage 5 reports the real .venv/bin/python scripts/plans.py audit output after the status edit; a claim without that output is not enough. Write toward these gates from Stage 0.

Core beliefs

1. Conformance > novelty. Default is to follow existing decisions and patterns. A new shape is only justified when an existing decision is wrong-for-this-case (/decide --supersede) or the pattern doesn't cover the situation.
2. Material forks are explicit, not buried. Every choice with 2+ defensible answers gets surfaced in §6. The threshold from /decide: a fork is material if it (a) constrains future work, (b) excludes an alternative explicitly, or (c) sets an expiration.
3. Smells avoided are as load-bearing as patterns followed. If the natural shape of the work would create an omnibus module / a stringly-state / a layer violation, §5 says so and §6 records the fork "do this anyway and accept the smell" vs "redesign to avoid".
4. Inline /decide invocations are encouraged. If you can write the ADR Decision sentence right now without speculation, invoke /decide <slug> inline and capture the assigned id. Otherwise, record the fork in §6 with (decision pending).

Scope (this skill itself)

• Project root: this worktree's root.
• Python: .venv/bin/python. The registry scripts parse YAML frontmatter through PyYAML from requirements.txt; the venv is part of the contract.
• Read: ai-docs/plans/<name>.md, ai-docs/decisions/ (full), .claude/docs/canonical-patterns.md, .claude/docs/architectural-smells.md.
• Write: ai-docs/plans/<name>.md (§5-6 + status bump).
• MAY invoke: /decide <slug> for forks that can be authored inline.

Pipeline

Stage 0 — Setup

PLAN_NAME="<arg>"
PLAN_PATH="ai-docs/plans/${PLAN_NAME}.md"

Verify plan exists and status: impacted. If status is draft or scoped, abort and recommend the matching earlier-stage skill. If status is architected+, abort and recommend the next-stage skill.

Stage 1 — Load constraints

.venv/bin/python scripts/decisions.py audit --json
.venv/bin/python scripts/decisions.py list --json

Read .claude/docs/canonical-patterns.md and .claude/docs/architectural-smells.md end-to-end. Read every ADR file under ai-docs/decisions/ whose applies_to: overlaps with the subsystems in the plan's §3.

Stage 2 — Walk the impact map

For each touched piece in §3 (subsystem, model, route, service):

• Decision check. Is there an ADR that constrains how this can be built? If yes, list it; the implementation must conform or the plan must include a /decide --supersede step.
• Pattern check. Does a canonical pattern apply? List the anchor. The implementation must follow it.
• Smell check. Would the natural shape create a known architectural smell? If yes, record the smell name and the avoidance strategy.

Build a working list of three columns: (target, conformance, smells_to_avoid).

Stage 3 — Identify material forks

For each design decision the implementation will face, classify:

• Resolved by existing decision. No fork — record the conformance.
• Resolved by pattern. No fork — record the pattern anchor.
• Material fork — can author inline. You can write the ADR's Decision sentence right now without speculation. Invoke /decide <slug> and capture the assigned id; add the id to §5 conformance.
• Material fork — pending. Needs more investigation, prototype, or stakeholder input. Add to §6 as (decision pending). If 2+ alternatives are defensible and the cost of being wrong is high, recommend /design-it-twice <fork-slug> in the §6 entry — it spawns 3 divergent designers and produces a comparative analysis you can feed into /decide later.
• Material fork — supersedes existing. The natural answer contradicts an existing decision. Surface to user; the resolution is either (a) /decide --supersede NNNN, (b) drop the work that caused the conflict (re-run /scope-feature), or (c) take an exception (record in §5).

Stage 4 — Write §5-6 of the plan

Edit ${PLAN_PATH} to fill §5 (Architecture Fit) and §6 (Open Decisions) from the working list:

## 5. Architecture Fit

**Decision conformance.**
- ADR `NNNN` (`<title>`) — _how the implementation conforms_
- ADR `NNNN` (`<title>`) — _exception with one-line justification_

**Pattern alignment.**
- `<anchor>` — _where in the implementation this lands_

**Smells avoided.**
- `<smell-name>` — _avoidance strategy_

**Smells accepted (with justification).**
- `<smell-name>` — _why we accept it (link to §6 fork if pending)_

## 6. Open Decisions

_Material forks not yet resolved. Each blocks `/plan-spec` until
either authored as an ADR or explicitly waived._

**P0 — must resolve before promotion.**
- `<fork-name>` — _alternatives_; _recommended `/decide` slug_

**P1 — should resolve before implementation.**
- `<fork-name>` — _alternatives_; _can be deferred to `/refactor-subsystem`_

**Authored inline.**
- ADR `NNNN` (`<title>`) — _written during this run_

Stage 5 — Advance status

Edit the frontmatter status: line to architected.

.venv/bin/python scripts/plans.py audit

Stage 6 — Summarize

Report to the user in ≤10 lines:

• Path to the plan.
• ADRs conformed-to (count by id).
• Patterns aligned (count by anchor).
• Smells avoided (count) and accepted-with-justification (count).
• ADRs authored inline this run (ids).
• Open P0 forks count + names — these BLOCK /plan-spec.
• Open P1 forks count.
• Recommended next command:
  • If P0 forks exist: /decide <slug> for each, then /plan-spec <plan-name>.
  • If clean: /plan-spec <plan-name> directly.

Non-goals

• Authoring ADRs as a side effect — /decide is the only way (this skill MAY invoke /decide inline but never writes to ai-docs/decisions/ directly).
• Scaffolding the spec (that's /plan-spec).
• Editing canonical-patterns.md or architectural-smells.md.
• Implementing the feature.

When things go sideways