fix: arm emergency shrink on upstream failure to break relay-5xx deadlock (#11)

[ranxianglei]

Problem (#11)

zcode user on a justwoker relay channel: every request for claude-opus-5 returns 500 after installing bili. Log shows:

• {"error":{"type":"new_api_error","message":"upstream error: do request failed"}} — the relay's own error (relay → its upstream failed), fixed ~31s timeout, plus one Cloudflare 522
• The session was huge: 676 messages, ~250K tokens vs a 200K window
• Other channels in the same log (openrouter ox-alpha, opencode.ai) worked fine, EMERGENCY compression fired there

Deadlock: compression triggering depends on the upstream usage report (lastInputTokens). A failed request never reports usage → the proxy re-sends the same ~250K payload on every retry → the relay fails it again → forever. The session can never recover through bili.

Fix

Arm the emergency shrink on failures with a local estimate of the body actually sent:

• armFailureShrink() (src/server.ts) — estimateTokensFast(body) raises session.stats.lastInputTokens if larger, then markDirty (error paths return before forward()'s trailing save). Deliberate exception to the "tokenCount must be real usage" invariant: it only RAISES the value (lower bound → compress earlier, never later), the kernel no-ops below truncate.threshold, and the next successful usage report overwrites it.
• Fires on: upstream 5xx responses (generic relay errors carry no overflow signature, so this is the only self-heal path) and network-level fetch failures (socket reset, timeout abort) for non-GET/HEAD.
• Excluded: 4xx (auth/quota errors must not distort the usage signal); overflow 400s keep the existing learned-window path.

Next turn, processTurn sees usage ≥100% → the kernel's emergency nudge + emergency-truncate node truncate large old tool results server-side (no model cooperation — critical, because the model never responds in this state). The resent payload shrinks below the relay's tolerance and the session recovers.

Tests

tests/e2e-relay-5xx-selfheal.test.ts (2 new e2e tests, mirroring the overflow-selfheal harness):

1. 500 → arm → truncate → recover: oversized history → relay 500 (passed through verbatim) → session armed with local estimate → next request's forwarded payload contains [truncated for context space], shrank, upstream 200 → real usage report overwrites the armed value
2. 401 does NOT arm: auth errors leave lastInputTokens untouched

Full suite: 567 tests pass, typecheck + build clean.

[github-actions]

📦 Built Package Artifact

Branch: 2026-08-24_fix-relay-5xx-deadlock (06666f0)

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npm install -g billion-context@pr-229

Each push to this PR publishes a new version under the pr-229 npm tag.

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1. Download the artifact from the Actions run
2. Extract the tarball and install:

tar xzf billion-context-pr229.tgz
npm install -g package

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