fix(tui): actionable File edit diagnostics and stale-line-number tolerance (#5003)

[SparkofSpike]

Summary

Fixes #5003. The report described a model repeatedly failing to apply large
(100+ line) replacements to a C file with Chinese comments and CRLF line
endings: 15+ failed File tool attempts, 3 full git checkout rollbacks,
and an eventual workaround via an external Python script. All four failure
modes are addressed so the tools either succeed or fail with diagnostics the
model can act on.

Changes

• edit_file: search == replace now sizes the payload and offers recovery —
  the error reports character/line counts, names the root cause (replace
  copied verbatim from search), and recommends apply_patch for large
  multi-line rewrites, so the model self-corrects instead of retrying the
  same no-op call.
• edit_file: Search string not found previews the search text — the
  error shows the first 3 lines of the search payload (80 chars per line), so
  the model can compare what it searched for against the file's contents.
• edit_file: C/C++ preprocessor conditional balance check — a replace
  must preserve the net #if/#ifdef/#ifndef vs #endif balance of the
  search span, catching the truncated #if 0 edit that previously applied
  with success and orphaned an #endif. Balanced local edits (e.g. a one-line
  #if 0 → #if 1 toggle) are unaffected.
• apply_patch: stale-line-number relocation — when positional fuzz fails
  and the hunk carries at least MIN_ANCHOR_LINES (4) expected lines, the
  hunk is relocated to a unique whole-file context match; ambiguous context
  (multiple matches) is refused with the candidate lines listed instead of
  guessing.
• apply_patch: clearer failure hints and relocation reporting — NoMatch
  now mentions that line numbers may be stale after earlier edits and
  suggests re-reading the file; relocated hunks are reported in
  PatchResult/FileSummary and the summary message.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Tests

Testing

• cargo fmt — clean (no diffs)
• cargo clippy -p codewhale-tui --bin codewhale-tui --locked — no new warnings from this change (5 pre-existing warnings live in crates/tui/src/tui/views/fleet_setup.rs, untouched)
• cargo test -p codewhale-tui --bin codewhale-tui --locked tools:: — 1374 passed, 0 failed (includes 6 new tests: relocation, ambiguous context, short-anchor no-relocation, and an end-to-end CRLF + Chinese-comment scenario)
• Manual verification on the rebuilt binary — all six issue scenarios pass:
  search==replace diagnostics, Chinese+CRLF replacement, #if truncation
  rejection, search preview, stale-line relocation, ambiguous-context refusal

Note: the full --workspace gate was not run in this session; the focused
codewhale-tui tool gates above were executed and passed.

Checklist

• Updated docs or comments as needed (change sites reference 针对中长文本的一段write功能出现严重反复。详见transcript #5003)
• Added or updated tests where relevant (6 new tests in apply_patch.rs/file.rs)
• Verified TUI behavior manually if UI changes (scenario walkthrough on rebuilt binary)
• Harvested/co-authored credit uses a GitHub numeric noreply address

Related Issues

Closes #5003

[SparkofSpike]

PTAL @Hmbown

the Lint check only fails at check-runtime-contract-budget with failed to download assert-json-diff v2.0.2 under --offline. This is a fork-PR limitation, not a code issue: fork PRs run with a read-only token (GITHUB_TOKEN Permissions: Contents: read), so Swatinem/rust-cache restores nothing (No cache found), while the checker forces Cargo offline. The identical cache key on main restores fine and the same step passes on main (run 30632266911). Other fork PRs (e.g. #5006) hit the same failure. The branch's Cargo.lock is byte-identical to main, so the merged result should be green on main CI.

Could you take a look when you have a moment? Happy to adjust if anything comes up.

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