Merge branch 'split/session-persistence' into split/agent-factory

# Conflicts:
#	docs/adr/README.md
#	packages/agent-loop/package.json
#	yarn.lock

docs/adr/0007-quality-gates.md

@@ -13,7 +13,7 @@ Every AGENTS.md promise gets a command that exits non-zero, wired into git hooks
 - Max-strict TypeScript (`noUncheckedIndexedAccess`, `exactOptionalPropertyTypes`, …); tests and examples typecheck in CI via `tsconfig.typecheck.json` (vendored packages resolve as built declarations).
 - ESLint strict-type-checked + @stylistic (the house style, enforced); vendored code excluded.
 - Per-file 100% coverage on `packages/*/src` (v8); unreachable defensive guards carry `/* v8 ignore */ ` with stated reasons instead of deletion.
-- knip (dead code/deps), publint (package correctness), yarn constraints (workspace rules: private, cordis peer+dev, uniform version, ESM).
+- knip (dead code/deps), publint (package correctness), workspace constraints (workspace rules: private, cordis peer+dev, uniform version, ESM).
 - lefthook pre-commit (lint staged, typecheck, vendor-manifest guard) and pre-push (tests, hygiene); CI runs the full matrix on node 24/26 plus a demo smoke test driving the echo-agent end to end.
 
 ## Consequences

docs/adr/0008-tsdown-over-dumble.md

@@ -6,16 +6,16 @@ Status: accepted (2026-06-11)
 
 The initial build used **dumble**, the cordiverse zero-config esbuild wrapper that upstream Cordis itself builds with — maximum alignment with the vendored packages' conventions (it reads each package.json and infers entries/formats from the `exports` field). But dumble is a liability as a load-bearing tool in this repo: v0.2.x, ~530 npm downloads/week, effectively one maintainer, and we were invoking it through a custom orchestration script (`scripts/build.ts`) because it has no workspace mode.
 
-Build output currently matters only for `yarn build` + publint (nothing publishes yet; dev/test/demo run unbuilt via tsx), so the switching cost is at its lowest now and only grows once packages publish.
+Build output currently matters only for `pnpm run build` + publint (nothing publishes yet; dev/test/demo run unbuilt via tsx), so the switching cost is at its lowest now and only grows once packages publish.
 
 ## Decision
 
 Replace dumble with **tsdown** (rolldown-based, ~2.5M downloads/week, VoidZero-backed, actively released):
 
-- Root `tsdown.config.ts` with `workspace: ['vendor/*', 'packages/*']` (explicit globs, not `workspace: true`, which would also pick up `examples/*` — they have package.json files but are not yarn workspaces).
+- Root `tsdown.config.ts` with `workspace: ['vendor/*', 'packages/*']` (explicit globs, not `workspace: true`, which would also pick up `examples/*` — they have package.json files but are not pnpm workspaces).
 - Shared shape: entry `src/index.ts`, `outDir: 'lib'`, ESM, `platform: node`, `target: es2024`, `fixedExtension: false` (keeps `.js` for `"type": "module"` packages), `dts: false` (tsc -b owns declarations), `clean: false` (lib/ holds tsc's .d.ts output).
 - Two per-package overrides in vendor/ (ours, like the regenerated tsconfigs; logged in vendor/README.md): schemastery (dual `.mjs`/`.cjs` via `outExtensions`), logger-console (two single-entry passes so the shared base class is inlined into each entry instead of a hash-named chunk, matching upstream's published shape).
-- `scripts/build.ts` deleted; `yarn build` = `tsc -b && tsdown`.
+- `scripts/build.ts` deleted; `pnpm run build` = `tsc -b && tsdown`.
 
 Alternatives considered: **direct esbuild script** (most established engine, zero wrapper risk, but hand-maintains the per-package spec table tsdown's workspace mode gives us); **pkgroll** (closest drop-in philosophically, but 78k dl/wk and Rollup-based — strictly weaker maintenance story than tsdown); **keep dumble** (perfect upstream alignment, unacceptable bus factor).
 

docs/adr/0014-doc-sync-enforcement.md

@@ -13,7 +13,7 @@ Two gates, mirroring the existing `scripts/` style (tsx ESM, one job each):
 1. **`doc-typecheck`** extracts every fenced ` ```ts ` block from `README.md`, `docs/**`, and `packages/*/README.md`, writes them to a temp project, and compiles with `tsc --noEmit`. The temp tsconfig copies only resolution-relevant options and the workspace `paths` map from `tsconfig.typecheck.json` (vendor → built `lib`, harness → `src`) — resolving vendor to `lib` is essential, or tsc type-checks raw vendor source and floods the run. A block that is a deliberate sketch opts out with an explicit ` ```ts ignore-check ` info string; the script reports the opt-out ratio and fails if it exceeds half, so the escape hatch can't quietly become the norm.
 2. **`verify-event-taxonomy`** extracts the event names from the `interface Events` blocks across `packages/*/src` and from the taxonomy table in `docs/architecture.md`, and asserts the two sets match exactly. Verify, don't generate: the table keeps its hand-written Mode/Purpose columns; only the set of names is checked. (Landing this surfaced three events the table had been missing — `tools/change`, `llm/adapter-change`, `system-prompt/change`.)
 
-Both run via a shared `doc-sync` package.json script that the lefthook pre-push hook and CI both invoke (ADR 0007: hooks and CI call the same scripts, so the gate fires locally before a push — not only after it). They run after `yarn typecheck` (which emits the vendor `lib/` that doc-typecheck resolves against). API-extractor golden reports (RFC 006 part 3) were deliberately **deferred** — low value for an internal monorepo where reviewers already see the source diff, and a heavy, finicky dependency.
+Both run via a shared `doc-sync` package.json script that the lefthook pre-push hook and CI both invoke (ADR 0007: hooks and CI call the same scripts, so the gate fires locally before a push — not only after it). They run after `pnpm run typecheck` (which emits the vendor `lib/` that doc-typecheck resolves against). API-extractor golden reports (RFC 006 part 3) were deliberately **deferred** — low value for an internal monorepo where reviewers already see the source diff, and a heavy, finicky dependency.
 
 ## Consequences
 

docs/adr/0016-pnpm-over-yarn.md

@@ -0,0 +1,37 @@
+# ADR 0016: pnpm as the package manager instead of Yarn 4
+
+Status: accepted (2026-06-16)
+
+## Context
+
+The repo shipped on **Yarn 4** with the `node-modules` linker — a deliberately conservative choice that behaves like npm's flat layout while giving us Yarn's workspaces and `yarn constraints`. It worked. But Yarn 4's Plug'n'Play heritage makes the `node-modules` linker the off-the-beaten-path mode, and the broader JS ecosystem — tooling defaults, CI actions, Corepack examples, contributor familiarity — increasingly centers on pnpm. For a repo that is built primarily by agents and read by occasional human contributors, "the package manager most tools and people expect" has real value: fewer surprises, better-trodden failure paths, more copy-pasteable answers.
+
+The switching cost is at its lowest right now. Nothing publishes from this repo yet (every package is `private: true`); dev/test/demo all run **unbuilt** via tsx, so the package manager only has to (a) resolve and link `node_modules`, (b) run the workspace scripts, and (c) enforce the workspace constraints. The one Yarn-specific asset is `yarn.config.cjs` (the `@yarnpkg/types` constraints engine), which is small and mechanical to re-express. This mirrors the reasoning in [ADR 0008](0008-tsdown-over-dumble.md): swap a load-bearing tool for the healthier-ecosystem option while the blast radius is still small.
+
+## Decision
+
+Adopt **pnpm 11.7.0**, pinned via the `packageManager` field and installed through Corepack (same mechanism Yarn used):
+
+- **Workspaces** move from the `package.json` `workspaces` array + `.yarnrc.yml` to `pnpm-workspace.yaml` (`vendor/*`, `packages/*` — the same globs; `examples/*` stay non-workspace, matching the prior setup and tsdown's explicit globs).
+- **Strict symlinked linker** (pnpm's default) replaces Yarn's hoisted `node-modules` linker. We deliberately add **no** `node-linker=hoisted` / `shamefully-hoist` escape hatch: pnpm's non-flat `node_modules` makes phantom dependencies (importing an undeclared transitive dep) fail loudly, which is a *feature* for a repo whose whole quality story is mechanical gates ([ADR 0007](0007-quality-gates.md)). The gate suite — typecheck, lint, test, build, knip — is the safety net that proves no such phantom imports exist.
+- **Build-script allowlist.** pnpm 10+ does not run dependency lifecycle scripts unless allowlisted. `pnpm-workspace.yaml` carries an explicit `allowBuilds` map (`esbuild`, `lefthook`, `@google/genai`, `protobufjs`) — the same supply-chain-hardening posture the repo already takes toward model/tool output, now applied to install-time code execution. `peerDependencyRules.allowedVersions.typescript: '>=5 <7'` silences benign peer-range warnings for the in-repo TypeScript.
+- **Constraints become package-manager-independent.** `yarn.config.cjs` (which imported `@yarnpkg/types` and used `Yarn.workspaces()` / `workspace.set()`) is replaced by `scripts/check-workspace-constraints.ts`, a plain tsx script run as `pnpm run constraints`. It enforces the identical invariants — every package `private: true`; `@deepseek-ai/dsh-*` packages declare `cordis` as both a peer- and dev-dependency with matching ranges, `version: 0.0.1`, `type: module`; vendored packages checked for privacy only — over the same `vendor` + `packages` scope.
+- All `yarn …` verbs across CI, lefthook hooks, `package.json` scripts, and docs become `pnpm …` / `pnpm run …`. `yarn.lock` → `pnpm-lock.yaml` (lockfile v9). `.gitignore` swaps `.yarn/` for `.pnpm-store/`. Vendored READMEs (e.g. `vendor/cordis/README.md`) keep their upstream `yarn` examples untouched per the Vendoring Policy.
+
+Alternatives considered: **keep Yarn 4** (zero churn, but bets on the less-traveled linker mode and a constraints engine tied to one package manager); **npm workspaces** (ubiquitous, but no constraints story and weaker monorepo ergonomics); **pnpm with hoisted linker** (smoother migration, but throws away the phantom-dependency safety that is the main correctness reason to move).
+
+## Consequences
+
+The constraints check loses Yarn's auto-**fix** (`workspace.set()` could rewrite a manifest in place); the tsx script is check-only and exits non-zero with a message instead. This is acceptable — CI never ran `--fix`, and a one-line manual edit is rare. Contributors now `corepack enable` for pnpm rather than Yarn; `pnpm exec lefthook install` replaces `yarn lefthook install` (the `postinstall` hook still runs `lefthook install`).
+
+Performance (measured at migration time on the dev NFS filesystem; single-digit-run samples, high variance — directional, not a benchmark suite):
+
+| Scenario | Yarn 4 | pnpm 11 |
+|---|---|---|
+| Cold (empty cache/store, no `node_modules`) | ~14 s | ~16 s |
+| Warm relink (cache/store warm, `node_modules` removed) | ~12–14 s | ~15–22 s |
+| Frozen, `node_modules` present (no-op revalidate) | ~2–8 s | ~0.5–7 s |
+
+On a fast local disk pnpm's content-addressed store typically wins on cold/warm installs and, especially, on **disk footprint** across multiple checkouts (one global store hardlinked into every `node_modules` vs Yarn copying ~279 MB per worktree — some devs regularly keep ~10 or more worktrees for this repo). That dedup advantage did **not** show in the migration-time numbers above because the test store and `node_modules` sat on different filesystems, defeating hardlinks; on a single-filesystem dev box or CI cache it applies. The honest summary: install speed on our NFS dev filesystem is a wash within noise; the move is justified by ecosystem alignment, phantom-dependency safety, and cross-checkout disk dedup — not by a raw install-time win.
+
+All quality gates (constraints, typecheck, lint, doc-sync, test:coverage at 100%, build, knip, publint, echo-agent demo smoke) pass unchanged on pnpm, which is the correctness proof that the linker swap introduced no phantom-dependency breakage.

docs/adr/0017-turn-enclosure-invariant.md

@@ -4,7 +4,7 @@ Status: accepted (2026-06-15)
 
 ## Context
 
-The durable JSONL backend ([ADR 0016](0016-session-persistence.md)) uses the **turn** as its crash-recovery boundary: `load` returns events only up to the last complete `turn/end`, and the first post-load `append` truncates whatever follows as a never-committed crash tail. This is safe only if nothing *legitimately* durable can sit after the last `turn/end`.
+The durable JSONL backend ([ADR 0018](0018-session-persistence.md)) uses the **turn** as its crash-recovery boundary: `load` returns events only up to the last complete `turn/end`, and the first post-load `append` truncates whatever follows as a never-committed crash tail. This is safe only if nothing *legitimately* durable can sit after the last `turn/end`.
 
 That assumption did not hold. Two paths recorded events outside any turn:
 
@@ -29,7 +29,7 @@ The serializability invariant is enforced at the same source boundary (`Session.
 
 ## Consequences
 
-The turn is now the *single* durability/replay boundary, so [ADR 0016](0016-session-persistence.md)'s "last `turn/end` = commit point" rule is complete, not merely sufficient: a backend can discard everything after the last `turn/end` with zero risk of losing between-turn context, because there is no between-turn context. `scanLog` stays simple (no partial-turn boundary walk), and an idle background-task notice survives persist + resume.
+The turn is now the *single* durability/replay boundary, so [ADR 0018](0018-session-persistence.md)'s "last `turn/end` = commit point" rule is complete, not merely sufficient: a backend can discard everything after the last `turn/end` with zero risk of losing between-turn context, because there is no between-turn context. `scanLog` stays simple (no partial-turn boundary walk), and an idle background-task notice survives persist + resume.
 
 Costs: `agent.inject()` while idle now writes three log lines instead of one, and the derived history gains a turn that carries only injected context (no assistant output) — `deriveMessages()` already derives purely by event type, so this renders identically. The `injection` trigger is a new on-disk vocabulary value; like every `SessionEventMap`/`TurnTriggerMap` addition it is part of the frozen format. Event ordering within a turn changed (`turn/start` now precedes `user/message`), which is observable to anything that asserted the old order — the loop's own tests were the only such consumers.
 

docs/adr/0018-session-persistence.md

@@ -1,4 +1,4 @@
-# ADR 0016: Session persistence as an abstract service over the existing `SessionEvent`
+# ADR 0018: Session persistence as an abstract service over the existing `SessionEvent`
 
 Status: accepted (2026-06-15)
 

docs/adr/README.md

@@ -27,5 +27,6 @@ Do NOT write an ADR for: a mechanical or local choice (a variable name, a one-fi
 | [0013](0013-property-based-testing.md) | Property-based testing for protocol-shaped code | accepted |
 | [0014](0014-doc-sync-enforcement.md) | Doc-sync enforcement (doc code blocks + event taxonomy) | accepted |
 | [0015](0015-structured-error-taxonomy.md) | Structured error taxonomy (HarnessError base) | accepted |
-| [0016](0016-session-persistence.md) | Session persistence as an abstract service over the existing `SessionEvent` | accepted |
+| [0016](0016-pnpm-over-yarn.md) | pnpm as the package manager instead of Yarn 4 | accepted |
 | [0017](0017-turn-enclosure-invariant.md) | Every session event is enclosed in a turn | accepted |
+| [0018](0018-session-persistence.md) | Session persistence as an abstract service over `SessionEvent` | accepted |