fix(tangle): bound tool output as content, not as metadata

[drewstone]

Problem

validatedSandboxPromptResult holds every field except response/text/finalText to the metadata bound, CONTRACT_MAX_STRING_LENGTH = 16,384 characters per string.

toolInvocations carries whatever a tool returned. One webfetch of a paper or an API page is routinely tens or hundreds of kilobytes. It is content, not a field that describes the turn.

Meanwhile the Sandbox SDK serializes each tool value up to MAX_SERIALIZED_TOOL_VALUE_BYTES = 4 MiB (runtime-api-BcLo4lBU.js:63). Producer and consumer disagree by 256×: every tool result between 16 KiB and 4 MiB is written by one side and refused by the other.

Why it was expensive

The refusal does not fail the tool call. This validator runs inside the terminal result read — after the live stream drained and after the usage receipt was credited — so it converted a finished, fully paid turn into an unreconcilable retained execution, which a supervisor then reports as a child that did no work at all.

Measured 2026-09-11 in one Discovery Lab worktree:

• 143 of 199 children across 16 pursuits, every one at iterations: 0, ms: 0, under the single reason retained provider execution requires reconciliation before replacement.
• Per run: 9 of 11, 16 of 23, 17 of 21, 14 of 19. Zero pursuits with an observer journal were clean.
• The lanes that died were the literature enumerate and extract stages — the ones that fetch papers. Directors doing local work survived.
• Their six-stage sourcing graph blocked at whatever stage it reached in 24 of 24 invocations, producing zero charters.

Selection evidence: across 45 surviving children and 845 tool results, the result-length distribution decays smoothly and stops dead at exactly 16,384, with none at or above it and no pile-up at the bound (which truncation would produce).

Direct falsification against the shipped validator — the wall is exactly where the constant is:

  16384  (passes the bound)
  16385  REJECTED — value exceeds its JSON bound
  20000  REJECTED — value exceeds its JSON bound
 250000  REJECTED — value exceeds its JSON bound

Change

Add toolInvocations to the fields excluded from the metadata check. isBoundedEventContentJson was written for exactly this material — its comment says content "may contain a single large transcript or tool result" — and the whole record already passes it at CONTRACT_MAX_JSON_BYTES immediately above.

Tool output stays bounded: the content check still refuses an unbounded result. Every other field keeps its metadata limit.

Tests

One added to tangle-events.test.ts. It fails on the previous code with the exact production error, value exceeds its JSON bound. It pins the wall (MAX_STRING_LENGTH + 1 now passes), a realistic 200 KB fetch, the retained upper bound (2 MiB still refused), and that traceId keeps the metadata limit.

Provider suite 263 pass, typecheck clean. Patch version 1.1.8 → 1.1.9.

🤖 Generated with Claude Code