refactor(tool-fs): consolidate read rendering; drop the fs/observed try-catch

Two cohesion cleanups on the filesystem tool package:

- Fold window.ts + types.ts + formatReadOutput into one cordis-free
  read-render.ts. Line windowing, the FileReadOutcome shape, and output
  formatting are one concern (the read tool's rendering); splitting them across
  three files added no value. read.ts is now just the tool (schema + I/O).

- Drop observe.ts and emit fs/observed with a plain ctx.emit in read/write/edit.
  The event is contractually a synchronous, side-effect-only recorder
  (file-context's listener is a WeakMap.set), so the per-call try/catch guarded
  against a contract violation that cannot happen under the shipped listener —
  defensive code for an impossible case. The event contract (dsh-fs JSDoc,
  README, RFC) is updated to state the fire-and-forget semantics plainly.

docs/cordis-catalog/events-and-services.md

@@ -199,7 +199,7 @@ Source: [`packages/fs/fs/src/index.ts:117`](../../packages/fs/fs/src/index.ts)
 
 #### `fs/observed` — emit
 
-Record that an actor observed a target at a version, after a successful read/write/edit. Fire-and-forget. A listener MUST be a synchronous, side-effect-only recorder (`@deepseek-ai/dsh-file-context`'s is a `WeakMap.set`); the tool wraps the emit in a try/catch so a synchronous listener bug is logged and swallowed, never failing the already-completed mutation. cordis `emit` does not await listener promises, so this is not an async-error containment seam — async audit/telemetry does not belong here. No listener ⇒ nothing recorded. `actor` is the opaque tool-execution context.
+Record that an actor observed a target at a version, after a successful read/write/edit. Fire-and-forget (plain `emit`). A listener MUST be a synchronous, side-effect-only recorder (`@deepseek-ai/dsh-file-context`'s is a `WeakMap.set`): the tool does not guard the emit, so a listener that throws surfaces as the tool's `isError` result, and cordis `emit` does not await listener promises — async or fallible audit/telemetry does not belong here. No listener ⇒ nothing recorded. `actor` is the opaque tool-execution context.
 
 ```ts cordis-catalog
 'fs/observed'(target: FsTarget, version: FsVersion, actor: object | undefined): void

docs/core-data-structures/filesystem.md

@@ -4,7 +4,7 @@ The filesystem stack is split across four packages: a provider seam ([dsh-fs](..
 
 The model is **additive, not subtractive**: `ctx.fs` alone is a complete, unconstrained text-storage seam (`write` unconditionally creates-or-overwrites, `edit` unconditionally replaces literal text). `dsh-file-context` is a plugin that *adds* policy on top by deciding the `fs/*` waterfalls; removing it leaves the bare provider rather than breaking the tool, because the tool is not method-coupled to the policy. A deployment that loads `dsh-tool-fs` is expected to also load `dsh-file-context` so the default behavior is read-before-write/edit.
 
-Provider source: [`packages/fs/fs/src/types.ts`](../../packages/fs/fs/src/types.ts) and [`packages/fs/fs/src/index.ts`](../../packages/fs/fs/src/index.ts). Policy source: [`packages/fs/file-context/src/types.ts`](../../packages/fs/file-context/src/types.ts). Read-rendering source: [`packages/fs/tool-fs/src/types.ts`](../../packages/fs/tool-fs/src/types.ts).
+Provider source: [`packages/fs/fs/src/types.ts`](../../packages/fs/fs/src/types.ts) and [`packages/fs/fs/src/index.ts`](../../packages/fs/fs/src/index.ts). Policy source: [`packages/fs/file-context/src/types.ts`](../../packages/fs/file-context/src/types.ts). Read-rendering source: [`packages/fs/tool-fs/src/read-render.ts`](../../packages/fs/tool-fs/src/read-render.ts).
 
 ## Target identity and metadata (provider seam)
 

docs/rfc/implemented/architecture/2026-06-26-file-context-as-event-gate.md

@@ -96,10 +96,10 @@ interface Events {
   'fs/edit-expectation'(target: FsTarget, actor: object | undefined, next: () => { version: FsVersion } | undefined | Promise<{ version: FsVersion } | undefined>): Promise<{ version: FsVersion } | undefined>
   /**
    * Record that an actor observed a target at a version, after a successful
-   * read/write/edit. Fire-and-forget. Listeners MUST be synchronous, side-effect-
-   * only recorders (`dsh-file-context`'s is a WeakMap write); the tool wraps the
-   * emit in a try/catch so a synchronous listener bug is logged and swallowed,
-   * never failing the already-completed mutation. No listener ⇒ nothing recorded.
+   * read/write/edit. Fire-and-forget (plain emit). Listeners MUST be
+   * synchronous, side-effect-only recorders (`dsh-file-context`'s is a WeakMap
+   * write); the tool does not guard the emit, so a throwing listener surfaces as
+   * the tool's isError result. No listener ⇒ nothing recorded.
    * @mode emit
    */
   'fs/observed'(target: FsTarget, version: FsVersion, actor: object | undefined): void
@@ -112,19 +112,19 @@ The `fs/*` decision events are **unbound waterfalls dispatched by the tool** (li
 
 The tool keeps its model-facing schemas (`read`/`write`/`edit`, byte-for-byte unchanged) and prompt sections. The prompt guidance stays policy-first because a deployment loading the fs tools is expected to also load `dsh-file-context`: the model is still told to read before overwriting or editing, and any wording that says the "backend" requires that should be corrected to say the file-context policy requires it. The bare-provider fallback does not change the prompt stance.
 
-`dsh-tool-fs` gains the executor responsibilities relocated from the old `fileContext` method service, including **read windowing** (`window.ts`, `READ_MAX_BYTES`, `READ_MAX_LINE_LENGTH`, `FileReadOutcome`/`FileTextLine`, `STREAM_MIN_SIZE`), which is the tool's rendering detail now that the tool owns the read. Those read-windowing types and helpers move into `dsh-tool-fs`; the policy plugin must not remain a type dependency for the tool.
+`dsh-tool-fs` gains the executor responsibilities relocated from the old `fileContext` method service, including **read rendering** (`read-render.ts`: `buildWindow` + `formatReadOutput`, `READ_MAX_BYTES`, `READ_MAX_LINE_LENGTH`, `FileReadOutcome`/`FileTextLine`, plus `STREAM_MIN_SIZE` in `read.ts`), which is the tool's rendering detail now that the tool owns the read. Those read-rendering types and helpers move into `dsh-tool-fs`; the policy plugin must not remain a type dependency for the tool.
 
 `dsh-tool-fs` is a single root plugin that registers all three tools (`read`/`write`/`edit`), mirroring `dsh-tool-bash`. It injects `fs` (plus `tools`/`systemPrompt`), never `fileContext`. (The original proposal also exposed each tool as a `/read`/`/write`/`/edit` subpath plugin for focused deployments; that was dropped on implementation — no consumer needed a single-tool deployment, and the subpath publishing forced bespoke `tsdown`/`tsconfig`/`files`/workspace-constraint handling no sibling tool package carries. The per-tool registration helpers (`applyReadTool`/`applyWriteTool`/`applyEditTool`) remain internal modules the root plugin composes.)
 
 `stat` budget is minimized by letting the waterfall produce the expectation lazily — the bare default returns `undefined` (no guard) and never stats:
 
-- **read** — one `stat` (type + size routing + version), then `readText`/`streamText`, then `buildWindow`, then a contained `emit('fs/observed', target, info.version, exec)`. The post-read confirming `stat` from the old `fileContext.read` is dropped; a writer racing between the routing stat and the read can at worst make a *later* guarded edit spuriously `FS_STALE_VERSION` (fail-closed: the model re-reads, never writes against the wrong version, since `editText` re-checks in its lock).
-- **write** — `expectation = await ctx.waterfall('fs/write-expectation', target, exec, () => undefined)`, then `ctx.fs.writeText(target, content, expectation)`, then a contained `emit('fs/observed', target, outcome.version, exec)`. **Zero stat in the tool** with or without `dsh-file-context`.
-- **edit** — `expectation = await ctx.waterfall('fs/edit-expectation', target, exec, () => undefined)`, then `ctx.fs.editText(target, edit, expectation)`, then a contained `emit('fs/observed', target, outcome.version, exec)`. **Zero stat in the tool** in both cases: the bare default is `undefined` (unconditional edit), so the tool never stats to manufacture a basis. If the target is absent, the provider reports `FS_STALE_VERSION` even on the unguarded path.
+- **read** — one `stat` (type + size routing + version), then `readText`/`streamText`, then `buildWindow`, then an `emit('fs/observed', target, info.version, exec)`. The post-read confirming `stat` from the old `fileContext.read` is dropped; a writer racing between the routing stat and the read can at worst make a *later* guarded edit spuriously `FS_STALE_VERSION` (fail-closed: the model re-reads, never writes against the wrong version, since `editText` re-checks in its lock).
+- **write** — `expectation = await ctx.waterfall('fs/write-expectation', target, exec, () => undefined)`, then `ctx.fs.writeText(target, content, expectation)`, then an `emit('fs/observed', target, outcome.version, exec)`. **Zero stat in the tool** with or without `dsh-file-context`.
+- **edit** — `expectation = await ctx.waterfall('fs/edit-expectation', target, exec, () => undefined)`, then `ctx.fs.editText(target, edit, expectation)`, then an `emit('fs/observed', target, outcome.version, exec)`. **Zero stat in the tool** in both cases: the bare default is `undefined` (unconditional edit), so the tool never stats to manufacture a basis. If the target is absent, the provider reports `FS_STALE_VERSION` even on the unguarded path.
 
 The tool passes `exec` (the tool-execution context) as the `actor` argument on every dispatch, so `dsh-file-context` can derive its observed-state owner. The tool does not know whether the policy plugin is present: it always provides the bare default behavior in the `next` thunk, and `dsh-file-context` short-circuits the thunk before it runs in the default deployment.
 
-**`fs/observed` recording must never fail the tool, because it fires AFTER the mutation already succeeded** — a throw there becomes an `isError` result ([tools/index.ts](../../../../packages/core/tools/src/index.ts) — `ToolRegistry.execute` catches a tool throw into an error result), reporting failure for a write/edit that actually happened. The tool therefore wraps the dispatch in a try/catch that logs and swallows synchronous listener bugs (the established fire-and-forget pattern in [agent.ts](../../../../packages/core/agent-loop/src/agent.ts)). The event contract is intentionally narrower than "arbitrary observers": an `fs/observed` listener MUST be synchronous and side-effect-only — `dsh-file-context`'s listener is a `WeakMap.set`, which cannot throw under normal operation and returns no promise. Cordis `emit` does not await listener promises, so the try/catch is NOT an async-error containment mechanism; async audit/telemetry/listener work does not belong on this event. If layered or async observation is ever wanted, that is a new event with its own dispatch story.
+**`fs/observed` fires AFTER the mutation already succeeded**, via a plain `ctx.emit`. The event contract is intentionally narrow: an `fs/observed` listener MUST be synchronous and side-effect-only — `dsh-file-context`'s listener is a `WeakMap.set`, which cannot throw under normal operation and returns no promise. The tool does not guard the emit, so a listener that violates the contract by throwing would surface as the tool's `isError` result ([tools/index.ts](../../../../packages/core/tools/src/index.ts) — `ToolRegistry.execute` catches a tool throw into an error result) — reporting failure for a write/edit that actually happened. That is the price of keeping the event a plain fire-and-forget recorder: cordis `emit` does not await listener promises, so async or fallible audit/telemetry/listener work does not belong on this event. If layered or async observation is ever wanted, that is a new event with its own dispatch story.
 
 ## Policy plugin contract (`dsh-file-context`)
 
@@ -154,12 +154,12 @@ This amends — does not reverse — [the split-fs-seam RFC](../simplification/2
 
 ## Acceptance Criteria
 
-- The `dsh-tool-fs` root plugin injects `fs` (+ `tools`/`systemPrompt`), not `fileContext`; it calls `ctx.fs` directly and dispatches the `fs/write-expectation`/`fs/edit-expectation` waterfalls (passing `exec` as the actor) and the contained `fs/observed` emit. Read windowing lives in `dsh-tool-fs`. (No subpath plugins — see the Tool contract above.)
+- The `dsh-tool-fs` root plugin injects `fs` (+ `tools`/`systemPrompt`), not `fileContext`; it calls `ctx.fs` directly and dispatches the `fs/write-expectation`/`fs/edit-expectation` waterfalls (passing `exec` as the actor) and the `fs/observed` emit. Read rendering lives in `dsh-tool-fs`. (No subpath plugins — see the Tool contract above.)
 - `dsh-fs` declares the three events with `@mode` tags and an opaque `object` actor argument (no agent/session structure leaks into the provider vocabulary); the generated cordis catalog is regenerated.
 - `dsh-file-context` is a plugin, not a service: it does not register `ctx.fileContext`, has no public `read`/`write`/`edit`/`resolve` methods, and does not inject `fs`; it registers the three listeners, keeps observed-state, and has HMR/disposal coverage (dispose the fiber, assert the gate no longer rewrites).
 - **Bare-provider test**: a config WITHOUT `dsh-file-context` boots the `dsh-tool-fs` root plugin, and `read`/`write`(create AND overwrite)/`edit` work against the real `dsh-fs-local`; an `edit` of an unread existing file and an overwrite of an existing unread file both succeed (unconditional bare-provider behavior), proving the tool carries no `fileContext` dependency. A bare-provider edit of a missing target reports `FS_STALE_VERSION`. With `dsh-file-context` present, the same unread `edit` is rejected `FS_NOT_OBSERVED` and the same unread overwrite uses `createIfAbsent` (rejected on an existing file).
 - **Single-slot semantics**: a test registers a second `fs/edit-expectation` listener AFTER `dsh-file-context` and asserts it is NOT reached (first-wins short-circuit), and documents in a comment that a decider registered before/`prepend`ed would instead win — the slot is first-wins by convention, not an enforced invariant.
-- **Contained observed recording**: a test with a synchronously throwing `fs/observed` listener performs a write/edit and asserts the tool result is still success (the completed mutation is not turned into an `isError`). The event contract requires synchronous side-effect-only listeners; the try/catch is the synchronous backstop, not async rejection handling.
+- **Fire-and-forget recording**: `fs/observed` is emitted via a plain `ctx.emit` after the mutation succeeds; a listener is contractually synchronous and side-effect-only, so the tool does not guard it.
 - `dsh-fs` `writeText`/`editText` make `expected` optional (omit ⇒ unconditional); the `FsWriteExpectation` union is unchanged, and `dsh-file-context`'s guarded paths (`createIfAbsent`/`replaceIfVersion`/`{ version }`) behave exactly as today. A bare-provider test exercises an unconditional overwrite, an unconditional edit, and a missing-target edit reporting `FS_STALE_VERSION`.
 - Freshness is enforced by provider CAS when guarded: an edit after a stale read reports `FS_STALE_VERSION` (regression test); `dsh-file-context` performs no `stat`.
 - `stat` budget: read = 1, write = 0, edit = 0 — in the tool, with or without `dsh-file-context` (the bare default returns `undefined`, never stats). A test asserts neither write nor edit stats in the tool on either path.