fix(o87): preserve proxy connect cause; skip rdk-docs warm under HTTPS_PROXY

[QiaolongLi1201]

Summary

O87 (板上 P0): CONNECT 有、回答无 — preserve full failure cause, raise proxy connectTimeout, and skip eager rdk-docs npx warm under HTTPS_PROXY so default MCP-on does not squeeze the main gateway on a narrow reverse tunnel.

Board lock (/workspace/ux/board-o67-o70-baseline.md, tip 4b783fc7):

Condition	Result
Same tunnel, only HTTPS_PROXY, MOSS_NO_RDK_DOCS=1	11s useful answer PASS
Same tunnel, MCP (rdk-docs) on	CONNECT present but fails + truncated 网关原文：)

Acceptance (QA / PM, locked after #83)

1. Complete cause — forbid truncated 网关原文：)
2. Only HTTPS_PROXY: CONNECT ∧ useful answer even with default MCP on (must not squeeze main gateway)
3. Failures must not be mislabeled as timeout/auth
4. UX board matrix: default MCP vs MOSS_NO_RDK_DOCS=1

Fix

Cause-complete (priority 1)

• Classify UND_ERR_CONNECT_TIMEOUT / ConnectTimeoutError as network (never model timeout / auth /「换更快的模型」)
• Connection failures use attach='details' so chat keeps low-level cause (详细信息：…UND_ERR_…)
• Drop punctuation-only gateway leftovers (lone )) — never show 网关原文：)
• connection-error.ts: proxy-aware hint for undici connectTimeout (MOSS_CONNECT_TIMEOUT_MS)

MCP / tunnel contention (priority 2)

• EnvHttpProxyAgent connectTimeout 30s when proxy set (override via MOSS_CONNECT_TIMEOUT_MS; 0 = undici default)
• shouldEagerWarmRdkDocs(env): skip eager rdk-docs npx warm when HTTPS_PROXY/HTTP_PROXY set; first rdk-docs tool call still starts the server

Does not touch src/safety/** or git-config-env.ts. Independent of #80 exit-hang sign-off.

Files

• src/provider/errors.ts
• src/provider/error-classify.ts
• src/provider/connection-error.ts
• src/provider/keep-alive-dispatcher.ts
• src/cli/rdk-docs-mcp.ts
• src/cli-main.ts
• test/o87-connect-without-answer.spec.mjs (new)
• test/error-classify-500.spec.mjs (minor assert align)

Tests

npm run check                                          # PASS (format + lint + typecheck)
node --test test/o87-connect-without-answer.spec.mjs   # 8/8 PASS
node --test test/error-classify-500.spec.mjs           # PASS
npm run test:filter -- --filter error-classify         # PASS (3 files)

Coverage:

• UND_ERR_CONNECT_TIMEOUT → network + Details, not timeout/auth
• lone ) → no 网关原文
• CONNECT-then-blackhole fixture → network + cause
• shouldEagerWarmRdkDocs false under proxy
• resolveConnectTimeoutMs 30s / override / 0

Base

• Rebased onto faa5c4e7 (main after docs(o66/o85): board proxy + RDK dependency guidance (README + doctor) #83 merge)
• Head: ae971f6e

Board (UX)

After CI green: re-run matrix — only HTTPS_PROXY, default MCP vs MOSS_NO_RDK_DOCS=1; lock CONNECT ∧ useful answer + complete cause on failure.

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