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/tool-fs/src/edit.ts

@@ -16,7 +16,6 @@ import type { Context } from 'cordis'
 import { defineTool } from '@deepseek-ai/dsh-tools'
 import type { DiffCallView, DiffResultView, ToolResult } from '@deepseek-ai/dsh-tools'
 import type { ContentBlock } from '@deepseek-ai/dsh-llm'
-import type { FsEditOutcome } from '@deepseek-ai/dsh-fs'
 import type {} from '@deepseek-ai/dsh-fs'
 import type {} from '@deepseek-ai/dsh-system-prompt'
 import { computeHunkDiffs, diffsFromMeta, type FsDiffMeta } from './diff.ts'
@@ -43,9 +42,9 @@ export function parseEditArgs(args: { file_path: string; old_string: string; new
   }
 }
 
-/** Format an edit outcome as a Claude-style model-facing success message. */
-export function formatEditOutput(displayPath: string, outcome: FsEditOutcome): string {
-  return outcome.replaceAll
+/** Format an edit success (single-match or replace-all) as a Claude-style model-facing message. */
+export function formatEditOutput(displayPath: string, replaceAll: boolean): string {
+  return replaceAll
     ? `The file ${displayPath} has been updated. All occurrences were successfully replaced.`
     : `The file ${displayPath} has been updated successfully.`
 }
@@ -91,7 +90,7 @@ export function applyEditTool(ctx: Context): void {
       // relativizes it).
       const diffs = computeHunkDiffs(input.filePath, outcome.before, outcome.after)
       return {
-        content: [{ type: 'text', text: formatEditOutput(target.displayPath, outcome) }],
+        content: [{ type: 'text', text: formatEditOutput(target.displayPath, input.replaceAll) }],
         meta: { diffs },
       }
     },