fix(server-tools): replay spent upstream bodies as real error statuses

[orangeboyChen]

Problem

An upstream rate limit surfaced to clients as status_code=500, Body already used instead of the real 429:

[CodeBuddy2API] Upstream request failed {
  route: "/v1/chat/completions",
  status: 429,
  detail: "{"code":6004,"msg":"您的使用量已超出频率限制..."}"
}

Cause

The route: "/v1/chat/completions" in that log is fetchChatCompletion's internal label, so the 429 came from inside the server-tool loop, not a plain chat request.

executeWebSearchLoop read the upstream body to check whether the model asked for a search, then returned that same Response object. A Response body can only be consumed once, so the route layer's second read — the one that builds the answer the client sees — threw Body is unusable: Body has already been read, and the 500 replaced the real status.

Confirmed against the unpatched tree: HTTP 500 {"type":"error","error":{"type":"api_error","message":"Body is unusable: Body has already been read"}}.

Fix

• web-search-loop.ts — clone before reading in both loop iterations, and rebuild the response from the drained body on failure so both reads work. The body is replayed verbatim rather than re-serialized, so an error detail that isn't valid JSON still reaches the client intact. content-length/content-encoding are dropped because the bytes are re-emitted, not re-encoded.
• anthropic.ts — the streaming bridge emitted a generic api_error at HTTP 200, hiding the upstream status from clients that key retry decisions on rate_limit_error. It now maps the upstream status through the same status→type table the non-streaming path already used, extracted as anthropicErrorType.

Result

path	before	after
Anthropic non-stream	500 api_error	429 rate_limit_error + upstream detail
Anthropic stream	200 api_error	200 + rate_limit_error + upstream detail
Chat completions	500 Body already used	429 + upstream detail

The streaming HTTP status stays 200 because the Anthropic SSE envelope is already committed by the time the failure arrives — the error type now carries the information instead.

Verification

3 new regression tests in tests/server/upstream-error-response.test.ts; all 3 fail on the unpatched tree and pass with the fix.

• bun run lint / format:check / typecheck / build — pass
• bun run test:ci — 670 tests pass, 94.46% statements
• bun run test:patch-branches — 92.80% (≥ 90% required)

Note

Based directly on main, not on fix/server-tool-loop-streaming. The fix cherry-picks cleanly and the full suite passes in both places, so it can merge independently of that in-flight work.

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[codecov]

Codecov Report

❌ Patch coverage is 97.95918% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.41%. Comparing base (80f4125) to head (53eaf6d).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #150      +/-   ##
==========================================
- Coverage   95.43%   95.41%   -0.02%     
==========================================
  Files          36       36              
  Lines        6329     6349      +20     
  Branches     1809     1813       +4     
==========================================
+ Hits         6040     6058      +18     
- Misses        289      291       +2     

Flag	Coverage Δ
unittests	95.41% <97.95%> (-0.02%)	⬇️

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