refactor(fs): prune write-only fields and the dead routing knob from the seam

The fs seam split left four pieces of pre-split surface populated on
every call and read by nobody:

- STREAM_MIN_SIZE + FsIoInternals.streamMinSize in dsh-fs-local: the
  backend has no read routing (readWholeText/streamWholeText are
  separate primitives the caller picks), and the real 10 MiB routing
  constant lives in dsh-tool-fs's read tool. Delete the dead mirror and
  the knob whose JSDoc claimed an override that did not exist; the
  remaining FsIoInternals knobs stay (the atomic-write tests use them).
- FsTarget.inputPath: a "diagnostics only" field every backend and test
  fake had to fabricate, with zero production readers (policy and error
  messages use targetKey/displayPath). listDir gave children the bare
  entry name, which was nobody's input.
- FsEditOutcome.replacements/.replaceAll: replacements had no reader
  (the single-match policy is enforced by the FS_AMBIGUOUS_EDIT /
  FS_EDIT_NOT_FOUND throws, whose message keeps the internal count);
  replaceAll only echoed the replace_all argument back to
  formatEditOutput, which now takes it from the parsed args. The
  outcome shrinks to { version, before, after }, parallel to
  FsWriteOutcome's backend-discovered fields. Emitted text is unchanged
  for both branches (no snapshot churn).
- FileReadOutcome.limit/.version: formatReadOutput renders
  offset/lines/totalLines/truncatedByBytes only, and the fs/observed
  emit uses info.version directly.

Backends shed four fabrication obligations and gain none. Doc pastes
(core-data-structures/filesystem.md), the dsh-fs README resolve row,
and the test fakes shrink with the types. RFC moved to
implemented/simplification and amended to the shipped shape
(FsEditSpec -> FsEditRequest name fix; manifest rows needed no change).

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

@@ -26,9 +26,6 @@ import { basename, dirname, join, resolve } from 'node:path'
 import { TextDecoder } from 'node:util'
 import { FsError, FsTargetKey, FsVersion } from '@deepseek-ai/dsh-fs'
 
-/** Files at or above this size stream their text; smaller files read whole. */
-export const STREAM_MIN_SIZE = 10 * 1024 * 1024
-
 const BINARY_SAMPLE_BYTES = 8192
 
 function isENOENT(error: unknown): boolean {
@@ -85,13 +82,11 @@ function versionOf(info: Stats): FsVersion {
 }
 
 /**
- * Test seam: lets specs force the streaming read path (via a small
- * `streamMinSize`) and pin the temp-file name (to prove exclusive-open
- * behavior) without a 10 MB fixture or a name race.
+ * Test seam: lets specs pin the atomic-write temp names (to prove
+ * exclusive-open behavior without a name race) and observe the staged temp
+ * file before it is renamed over the target.
  */
 export interface FsIoInternals {
-  /** Override {@link STREAM_MIN_SIZE} for read routing. */
-  streamMinSize?: number
   /** Override the generated private staging-dir name (relative to the target dir). */
   tempDirName?: (writePath: string) => string
   /** Override the generated temp-file name (relative to the private staging dir). */

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

@@ -41,7 +41,6 @@ import {
 import type { FsIoInternals } from './fsio.ts'
 
 export {
-  STREAM_MIN_SIZE,
   applyLiteralEdit,
   listDirectory,
   probe,
@@ -105,7 +104,7 @@ export class LocalFileSystem extends FileSystem {
 
   override async resolve(path: string, opts?: { cwd?: string }): Promise<FsTarget> {
     const local = await resolveLocalTarget(opts?.cwd ?? this.config.cwd, path)
-    return { inputPath: path, targetKey: local.targetKey, displayPath: local.displayPath }
+    return { targetKey: local.targetKey, displayPath: local.displayPath }
   }
 
   override async stat(target: FsTarget, signal?: AbortSignal): Promise<FsInfo | undefined> {
@@ -128,7 +127,7 @@ export class LocalFileSystem extends FileSystem {
     return entries.map(entry => ({
       name: entry.name,
       type: entry.type,
-      target: { inputPath: entry.name, targetKey: entry.target.targetKey, displayPath: entry.target.displayPath },
+      target: { targetKey: entry.target.targetKey, displayPath: entry.target.displayPath },
       ...(entry.version !== undefined ? { version: entry.version } : {}),
       ...(entry.size !== undefined ? { size: entry.size } : {}),
     }))
@@ -211,8 +210,6 @@ export class LocalFileSystem extends FileSystem {
 
       const after = await probe(target.targetKey)
       return {
-        replacements: edited.replacements,
-        replaceAll: edit.replaceAll,
         version: this.versionAfterWrite(after, target),
         // The LF-normalized before/after text (the applied-hunk diff basis);
         // line-ending restoration is a storage detail the diff ignores.