[JS-banana]

Problem

Since #652 (first released in v0.10.0), Antigravity requests fail with HTTP 400 when a loaded tool uses a TypeBox literal union. The in-tree example is subagent_check.evidence: anyOf branches contain const, which Cloud Code Assist rejects:

Invalid JSON payload received. Unknown name "const" at
'request.tools[0].function_declarations[8].parameters.properties[2].value.any_of[0]'

Setup role/browser literal unions expose the same failure. Related to #465 (the adjacent $ref problem, which this PR does not resolve).

Value

Restore the existing Antigravity tool path at the provider boundary, without rewriting each extension's schema or bypassing ordinary Pi tools.

Approach

• Rewrite a schema's const to a singleton enum inside sanitizeSchemaForCca, shared by Gemini and Claude request routes.
• A sibling enum is an additional constraint: retain only the constant, rather than unioning in other choices. Reject conflicting const/enum constraints locally with a clear error instead of advertising impossible choices.
• Treat enum values as literal data, preserving object values instead of recursively interpreting their keys as schemas.
• Preserve parameter names that match schema keywords. No dependency or host-version change.
• Rebased onto upstream main 0addb73963a924ee6daa5568151cd890b34e2999. Broader sanitization hardening remains in fix(ai-providers): harden CCA schema projection with safe literal handling #906.

Validation

Current head: dba602e9e5ab065699d0fdc3ae217b743bb83053. The 2026-11-03 CI refresh preserves exactly the source tree of ed55c898789168488cc59d7502960f483bae30b9; only commit metadata changed. The local results below were recorded on 2026-11-02 and are reused by identical tree identity, not presented as new local runs.

• node --test --experimental-strip-types tests/extensions/ai-providers/antigravity.test.ts: 63 passed. The corrected const/enum regression failed before the fix and passes afterward; includes contradictory constraints and structural object equality.
• bun run check: passed. Existing bundle-size warnings remain.
• bun run test: Node 2,455 tests, 2,445 passed / 8 skipped / 2 failed. Both failures are in tests/extensions/code-mode/index.test.ts.
• Baseline control: that exact Code Mode file on a clean detached upstream main@0addb739, using the same locked dependencies, reproduces the same two failures at the same assertions (1 passed / 2 failed). The full suite is therefore not reported as green.
• bun run test ui: 108 files, 1,632 tests passed (run separately because the normal command stops after Node failures).
• Real Pi 1.4.0, explicit source loading with -ne -a -e ./extensions/ai-providers/index.ts -e ./extensions/subagents/index.ts, ephemeral Session, built-in tools retained: google-antigravity/gemini-3.8-flash-high returned OK. without the schema 400. Installed npm OpenPI was not loaded into that run.
• git diff --check: passed.

Historical before/after request evidence in the original report remains historical; the real request does not establish that every literal kind or provider model was live-tested.

Previous-head CI run 41386858096 passed all runtime jobs and Web E2E shards but had one Windows UI 5-second timeout. The integration cannot rerun upstream Actions, so the author refreshed the unchanged branch tip with an explicit expected-SHA lease to request a fresh run. Current-head CI run 41610705003 completed successfully on 2026-11-03: all 17 jobs passed, including Windows UI, runtime, both Web E2E shards, and aggregate gates. No test was skipped, weakened, or given retries to obtain this result.

Impact

• User-visible: affected string-literal tools no longer cause the const-keyword 400.
• Model-visible: const becomes a singleton enum with the original allowed value; conflicting const/enum constraints fail locally.
• Runtime: no new tools, permissions, endpoint route, cache or lifecycle.
• Persisted config/data: none.
• Compatibility/risk: no dependency changes. This is not general JSON Schema validation or $ref support; broader wire projection is separately reviewed in fix(ai-providers): harden CCA schema projection with safe literal handling #906.