fix(fs): address review — rename to dsh-fs-policy, fs/*-intent events, RFC currency, ENOTDIR

Rename per review naming decisions:
- package dsh-file-context → dsh-fs-policy (dir, package name, plugin name,
  tsconfig refs, importers, type-equiv manifest, generated catalog + module-graph)
- events fs/write-expectation → fs/write-intent, fs/edit-expectation → fs/edit-intent
  (fs/observed unchanged); type FsWriteExpectation → FsWriteIntent, "expectation"
  wording → "intent" throughout
- exported FileContextExec → FsPolicyExec

Make the implemented RFCs describe what shipped, not the superseded designs:
the 2026-06-17 capability-seam + tool-schemas RFCs no longer place policy on
ctx.fs or use full/partial-view authorization, and the fsspec RFC's ctx.fileContext
service prose is rewritten to the fs/* event-gate reality (freshness-based auth).
Sharpen docs/rfc/implemented/AGENTS.md: a rename is a fact to fix IN PLACE — the
"new RFC" escape hatch is for macro decision reversals only, not renames.

Code fixes from review:
- fsio.ts resolveLocalTarget/probe translate ENOTDIR (a parent path segment is a
  file) into the structured FsError taxonomy instead of leaking a raw Node error;
  resolve reports FS_NOT_FOUND, probe reports absent. Regression tests proven to
  fail on the unfixed code.
- tool-fs HMR test now asserts prompt sections (not just tool schemas) are
  withdrawn on disposal.
- fs/observed is a plain (unguarded) ctx.emit: correct the fs-policy comment,
  filesystem.md, and tool-fs module doc that wrongly claimed the tool "contains"
  a throwing listener; a throw surfaces as the tool's isError result.
- drop the false "loaded by the default product config" claim (no config wires
  the fs tools yet), the duplicate ctx.bash service-map row, the stale
  FileReadRequest catalog link-map entry, and the fs/fs README EOF blank line;
  correct the dsh-fs package.json description.

packages/fs/fs-local/src/fsio.ts

@@ -5,7 +5,7 @@
  *
  * This is the PROVIDER layer: it hands back decoded whole-file text (validated
  * UTF-8, binary rejected) — never line windows or numbered lines, which are
- * model-facing read policy owned by `@deepseek-ai/dsh-file-context`. Large files
+ * model-facing read policy owned by `@deepseek-ai/dsh-fs-policy`. Large files
  * stream their text in chunks so a huge file never has to be held whole in
  * memory; the binary/NUL sample and cross-chunk UTF-8 decoding stay here.
  *
@@ -35,6 +35,16 @@ function isENOENT(error: unknown): boolean {
   return error instanceof Error && 'code' in error && error.code === 'ENOENT'
 }
 
+/**
+ * A path component that is expected to be a directory is a regular file (e.g.
+ * resolving `afile/child.txt` when `afile` is a file). Like `ENOENT`, the target
+ * cannot exist — so the resolution/probe paths treat it as "absent" rather than
+ * letting a raw Node error escape without the structured `FsError` taxonomy.
+ */
+function isENOTDIR(error: unknown): boolean {
+  return error instanceof Error && 'code' in error && error.code === 'ENOTDIR'
+}
+
 function isAbortError(error: unknown): boolean {
   return error instanceof Error && error.name === 'AbortError'
 }
@@ -119,6 +129,10 @@ export async function resolveLocalTarget(cwd: string, path: string): Promise<Loc
     // Prefer the file's own realpath (resolves a symlinked file to its target).
     return { displayPath, targetKey: FsTargetKey(await realpath(displayPath)) }
   } catch (error: unknown) {
+    // A path component is a file, not a directory (e.g. "afile/child.txt" where
+    // "afile" is a regular file): the target can neither exist nor be created,
+    // so surface the structured taxonomy instead of a raw Node ENOTDIR.
+    if (isENOTDIR(error)) throw new FsError(`cannot resolve "${displayPath}": a parent path segment is not a directory`, 'FS_NOT_FOUND')
     /* v8 ignore next -- non-ENOENT realpath failure needs a permission/IO fault; ENOENT falls through to ancestor resolution. */
     if (!isENOENT(error)) throw error
   }
@@ -150,8 +164,10 @@ export async function probe(absolutePath: string): Promise<PathInfo | null> {
     const type = info.isFile() ? 'file' : info.isDirectory() ? 'directory' : 'other'
     return { version: versionOf(info), mode: info.mode & 0o777, type, size: info.size }
   } catch (error: unknown) {
-    /* v8 ignore next 2 -- a non-ENOENT stat failure needs a permission/IO fault; surface it. */
-    if (!isENOENT(error)) throw error
+    // ENOENT (no such file) and ENOTDIR (a parent segment is a file) both mean
+    // the target is absent; any other stat failure is a real permission/IO fault.
+    /* v8 ignore next -- a non-ENOENT/ENOTDIR stat failure needs a permission/IO fault; surface it. */
+    if (!isENOENT(error) && !isENOTDIR(error)) throw error
     return null
   }
 }

packages/fs/fs-local/src/index.ts

@@ -21,7 +21,7 @@ import type {
   FsEditRequest,
   FsInfo,
   FsTarget,
-  FsWriteExpectation,
+  FsWriteIntent,
   FsWriteOutcome,
 } from '@deepseek-ai/dsh-fs'
 import {
@@ -120,7 +120,7 @@ export class LocalFileSystem extends FileSystem {
   override async writeText(
     target: FsTarget,
     content: string,
-    expected?: FsWriteExpectation,
+    expected?: FsWriteIntent,
     signal?: AbortSignal,
   ): Promise<FsWriteOutcome> {
     return this.withLock(target.targetKey, async () => {