fix(antigravity): handle native sign-in URLs on stderr - #9514

💭 I need to check the changed files: AcpSessionRuntime.ts, AntigravityAcpSupport.ts, and antigravityAuthSupport.ts to see what's relevant there.

1. browse_code — apps/server/src/provider/antigravityAuthSupport.ts

2. browse_code — apps/server/src/provider/acp/AcpSessionRuntime.ts

💭 Now I'm examining the changed region in AcpSessionRuntime, around lines 340-480.

3. browse_code — apps/server/src/provider/acp/AcpSessionRuntime.ts

4. browse_code — apps/server/src/provider/acp/AntigravityAcpSupport.ts

💭 I'm checking convention compliance for the changed lines in AcpSessionRuntime.ts, particularly around the onStderr type change and error handling — the Effect.catch usage looks fine since it handles the whole AcpError channel. Moving to AntigravityAcpSupport.ts, onStderr is always provided so that's fine too. For antigravityAuthSupport.ts, I'm considering the authSupportError helper and isAntigravitySignInRequiredError predicate — both appear pre-existing rather than newly added, so they shouldn't count as violations introduced by this PR since only changed lines matter here. I'm now checking the matchEffect behavior around parsing authorization URLs — onFailure swallows invalid-URL failures intentionally, but onSuccess failures from onAuthorizationUrl now propagate correctly, which differs from the old Effect.ignore behavior in a good way, and tests confirm this. I also check for added lint suppressions (none), confirm tests were added, and verify the raceFirst/Deferred usage with onStderr gating is a legitimate callback strategy rather than a dependency-injection issue. I want to double-check that using Effect.catch instead of catchTags is appropriate here since the entire AcpError channel is being handled, that Effect.fn returning a handler is fine, and that the stderr pipeline in AcpSessionRuntime correctly ignores errors after runForEach. I also want to verify matchEffect is a valid API in this Effect version and check how undefined unions are handled when parsing the URL.

5. browse_code — Is Effect.matchEffect used elsewhere in this repo (apps/, packages/) and does the installed effect version export Effect.matchEffect and Effect.catch? Show example usages with file paths.

💭 I don't see any clear convention violations in the diff. The stderr handler change makes the runtime always reject sign-in behaviorally, but tests were added to cover it, and the error handling uses an existing helper rather than introducing a new one, which seems consistent with the conventions. I'm settling on "All clear" as my conclusion, and need to make sure both the title and summary fields meet the minimum length requirements before calling complete_check.