docs: sync implementation docs and doc gates

AGENTS.md

@@ -73,6 +73,15 @@ packages/    Harness packages, grouped by role at packages/<group>/<pkg>/.
     bash/           abstract bash executor seam (ctx.bash) — interface only
     bash-local/     local-subprocess BashExecutor implementation
     tool-bash/      model-facing bash/bash_output/bash_kill tool schemas
+  compact/        compaction capability family
+    compact/        abstract compaction seam (ctx.compact); backend + tool deferred
+  subagent/       subagent capability family
+    subagent/       provider-registry seam (ctx.subagents)
+    subagent-inprocess/ shared in-process run driver (library, registers nothing)
+    subagent-spawn/ in-process fresh-child backend
+    subagent-fork/  in-process backend seeded from the parent's completed-turn prefix
+    subagent-acp/   out-of-process child over ACP
+    tool-subagent/  model-facing delegation tool over ctx.subagents
   todo/           todo/planning capability family
     tool-todo/      model-facing todo_write tool: writes the whole task list to
                     the session log (todo/write), rendered as a stdio checklist /
@@ -95,6 +104,7 @@ packages/    Harness packages, grouped by role at packages/<group>/<pkg>/.
                     feeds stdin lines to the agent (shared by the demos)
     llm-replay/     record/replay adapter: short-circuits llm/stream from a
                     recorded session JSONL (keyless snapshot tests)
+    subagent-mock/  scripted SubagentProvider for deterministic seam/tool tests
   util/           low-level zero-dependency utilities shared across groups
     brand/          type-only Branded<B> nominal-typing primitive (no runtime
                     code, no harness deps; owns the brand for cross-boundary ids)
@@ -181,7 +191,7 @@ pnpm run demo:acp   # run examples/acp-agent — the coding agent as an ACP
 CI is the backstop, not the first place a gate runs. Before you open a non-draft PR or move one from draft to ready, run the same gates CI runs, on your own tree, and confirm they pass — do not lean on CI (or a Codex pass) to discover a red gate you could have caught locally. The CI-equivalent local run is:
 
 ```sh
-pnpm run typecheck && pnpm run lint && pnpm run test:coverage && pnpm run test:snapshot && pnpm run doc-sync && pnpm run hygiene && pnpm run build
+pnpm run typecheck && pnpm run lint && pnpm run test:coverage && pnpm run test:snapshot && pnpm run doc-sync && pnpm run verify-module-graph && pnpm run build && pnpm run hygiene
 ```
 
 **`pnpm run test:coverage`, NOT `pnpm run test`, is the gating test command.** `pnpm run test` runs `vitest run` with no coverage; CI's node job runs `test:coverage`, which enforces a **per-file 100%** threshold on `packages/*/*/src`. A suite that is green under `test` can still fail CI on an uncovered line — and that uncovered line is often *dead code* the 100% gate is correctly flagging for deletion (see [§ Defensive patterns](#defensive-patterns-hard-won) "Line coverage is not behavior coverage"), not a missing test to bolt on. `hygiene` (knip + publint + workspace constraints + NodeNext types) and `test:snapshot` (keyless ACP replay) are likewise CI gates that `test` alone does not cover. When you rely on a Codex convergence pass for sign-off, check WHICH commands it ran: a pass that ran `test` but not `test:coverage`/`hygiene`/`doc-sync` has not exercised those gates.
@@ -256,9 +266,9 @@ Verbose documentation is fine **as long as docs and code stay strictly in sync**
 
 **Document the CURRENT state — the "what" and "why" — never the PROCESS or HISTORY of how it got there.** A comment, JSDoc, or doc paragraph describes what the code *is* and why it is that way, as if it had always been so. Do NOT narrate the change that produced it: no "previously X, now Y", "changed from", "used to", "this replaces", "the old map", "renamed", "moved here", "as of this PR", or "(was …)". **In particular, NEVER name the change unit a reader cannot see — the PR, commit, or stack position that introduced the code — in a comment, JSDoc, OR a test name/description.** A `// (PR D's per-agent teardown)` aside, a `* Tests for the cancel primitive (PR C).` module doc, or an `it('… identity no longer matters')` title that only makes sense relative to a prior design are all the same violation: the reader of the current tree has no "PR D" or "old design" to anchor against, and the reference rots the moment the stack merges. Name the *mechanism* (`the session's AgentHandle teardown`), not the PR. Such phrasing rots the instant the next change lands, and a reader of the current code does not need the diff narrated in prose — that belongs in the commit message, the PR description, or an RFC (the durable home for "why we moved away from X"). Write "the owner token lives on the task in the executor" — not "ownership *now* lives on the executor instead of a plugin-local map". When a contrast genuinely aids understanding (a non-obvious choice between live alternatives), frame it against the alternative as a standing fact ("stored on the executor, NOT the tool plugin, so it survives an HMR reload"), not against the codebase's past. The same rule governs review-fix commits: the *commit message* records what the review caught; the *code comment* it touches states only the resulting truth. RFCs (`docs/rfc/`, grouped into `proposed/` / `implemented/` / `rejected/`) record the *why* behind choices a future reader would otherwise re-litigate (the vendoring policy, event-sourcing, the schema DSL are the existing examples). A PR that introduces such a decision — a new third-party runtime dependency over the vendoring default, a cross-package contract, a security/isolation model, a deviation from a documented architecture rule — writes the RFC in `implemented/` **in the same PR**, and links it from the relevant code. A proposal for future work not yet built goes in `proposed/`. A PR whose changes are mechanical, self-evident, or already covered by an existing RFC needs none — do not manufacture an RFC for a routine change. When unsure, the test is: would a competent maintainer six months from now ask "why was it done this way?" and be unable to answer from the code alone? If yes, write it. See [docs/rfc/README.md](docs/rfc/README.md) for the naming scheme and [docs/AGENTS.md](docs/AGENTS.md) for the cross-link convention.
 
-**Markdown is not hard-wrapped**: write one line per paragraph and let the editor soft-wrap. Hard line breaks mid-paragraph make docs harder to edit and diff — a one-word change reflows and re-diffs the whole paragraph. This applies to prose only: leave fenced code blocks, tables, and list structure intact (a wrapped list item folds to one line per bullet). Code comments / JSDoc are exempt — they stay under the linter's column limit. `pnpm run verify-md-wrap` (part of `doc-sync`) enforces this across `README.md`, `docs/**/*.md`, `packages/*/*.md`, and `AGENTS.md` / `packages/AGENTS.md`; `pnpm run verify-md-links` (also part of `doc-sync`) checks that every relative cross-link in those files resolves.
+**Markdown is not hard-wrapped**: write one line per paragraph and let the editor soft-wrap. Hard line breaks mid-paragraph make docs harder to edit and diff — a one-word change reflows and re-diffs the whole paragraph. This applies to prose only: leave fenced code blocks, tables, and list structure intact (a wrapped list item folds to one line per bullet). Code comments / JSDoc are exempt — they stay under the linter's column limit. `pnpm run verify-md-wrap` (part of `doc-sync`) enforces this across `README.md`, `docs/**/*.md`, `packages/*/*.md`, and `AGENTS.md` / `packages/AGENTS.md`; `pnpm run verify-md-links` (also part of `doc-sync`) checks that every relative cross-link in those files plus `examples/**/*.md` and `.agents/skills/**/*.md` resolves.
 
-**Editing these instructions**: `AGENTS.md` is the real file; `CLAUDE.md` is a symlink to it (at the repo root and in `packages/`). Always edit `AGENTS.md` — never write through the `CLAUDE.md` symlink or replace it with a regular file.
+**Editing these instructions**: `AGENTS.md` is the real file; `CLAUDE.md` is a symlink to it (at the repo root and in `packages/` / `examples/`). Always edit `AGENTS.md` — never write through the `CLAUDE.md` symlink or replace it with a regular file.
 
 ## Vendoring Policy