docs(agents): add doc-current-state convention + sharpen the summary worked example (review)

Two review findings on the AGENTS.md additions:

- Add a convention to § Type Safety and Documentation: document the CURRENT
  state (what + why), never the PROCESS/HISTORY of how the code got there. No
  "previously/now/used-to/replaces/the old X" in comments or JSDoc — that rots
  on the next change and belongs in the commit message / PR / RFC. A standing
  contrast against a live alternative is fine; a contrast against the codebase's
  past is not.

- The "tests document behavior" worked example overstated the audit as "nothing
  in production read or wrote" the summary. The backends DID write it (JSONL
  sidecar, SQLite updated_at); what made it dead was no CONSUMER and no
  update() caller. Corrected so a future reader does not infer the write path
  never existed.

AGENTS.md

@@ -14,7 +14,7 @@ A passing test pins the behavior the code **currently** has — not necessarily
 
 Before you preserve a behavior solely to keep a test green, ask: is this behavior load-bearing (a real consumer depends on it, a contract promises it, a user observes it), or is it an artifact? If it's an artifact, **change the behavior AND its test together, in the same change, and say why in the PR** — do not contort new code to keep an obsolete assertion passing, and do not treat "but the test expects X" as a reason X must stay. Conversely, do not delete a test just because it is inconvenient: the discipline cuts both ways — you must show the *behavior* is dead, not merely that the test is in your way.
 
-The worked example is [Drop the mutable session summary](docs/rfc/implemented/2026-06-19-drop-mutable-session-summary.md): an entire `SessionSummary` type, a `SessionPersistence.update()` method, a JSONL sidecar, and SQLite columns existed and were exercised by their own contract test — yet nothing in production read or wrote any of it. The tests documented the behavior perfectly; the behavior was dead. Deleting the behavior and its tests together removed ~400 lines and erased a durability divergence the next refactor would have had to model. (This is the test-tier echo of "verify the world, not a synthetic stand-in" in § Defensive patterns: a test agrees with whatever it was written to assert; only a real consumer proves the behavior matters.)
+The worked example is [Drop the mutable session summary](docs/rfc/implemented/2026-06-19-drop-mutable-session-summary.md): an entire `SessionSummary` type, a `SessionPersistence.update()` method, a JSONL sidecar, and SQLite columns existed and were exercised by their own contract test — yet **nothing in production CONSUMED any of it, and `update()` had no production caller**. (The backends did *write* summary state — JSONL touched the sidecar after a durable append, SQLite bumped `updated_at` in the append transaction — but those writes fed only reads that nothing performed.) The tests documented the behavior perfectly; the behavior was dead. Deleting the behavior and its tests together removed ~400 lines and erased a durability divergence the next refactor would have had to model. (This is the test-tier echo of "verify the world, not a synthetic stand-in" in § Defensive patterns: a test agrees with whatever it was written to assert; only a real consumer proves the behavior matters.)
 
 ## Architecture
 
@@ -176,7 +176,7 @@ In the **core** packages (`packages/llm`, `packages/tools`, `packages/agent`, `p
 
 Verbose documentation is fine **as long as docs and code stay strictly in sync**. Out-of-sync docs are worse than no docs. **When you change code, update its docs in the SAME change** — grep the package README and the module/JSDoc comments for the old behavior (config keys, defaults, error codes, wire field names, event names) and fix every hit. CI runs `pnpm run doc-sync` (`doc-typecheck` + `verify-event-taxonomy` + `verify-md-wrap` + `verify-md-links`), which typechecks every fenced `ts` block in `README.md`, `docs/**/*.md`, and `packages/*/README.md`, verifies the event-taxonomy table against source, asserts no hard-wrapped prose paragraphs, and checks that every relative Markdown cross-link resolves — across those files plus `AGENTS.md` / `packages/AGENTS.md` — but that scope does NOT catch prose drift in `AGENTS.md` / `packages/AGENTS.md` / `packages/README.md` (config keys, defaults, error codes), so keeping those in sync remains on the author. Every module has a module-level doc comment explaining its role. Every exported class, interface, type, function, and non-obvious method has a JSDoc that explains semantics (not just the name) — contracts (what events fire when), disposal behavior, error behavior, and extension intent. Internal helpers get docs only where non-obvious. Prefer one-liners when one line suffices.
 
-**Write an RFC when — and only when — a PR makes a decision that is durable, contested, and surprising.** 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.
+**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 …)". 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/*/README.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.