Fix investigation snapshots, retries, and screenshot uploads

[MaggieAppleton]

Manual investigations could inherit an older investigation’s source commit, and screenshot requests had no upload tool. Failed attempts also left a local receipt that blocked Retry and hid the agent’s explanation behind missing-result.

New investigations now use the selected connector checkout. Retrying keeps that investigation’s original commit and creates a separate checkout for its new claim generation. Manual investigations can upload up to three screenshots of 1 MiB each through the existing authenticated image pipeline; HTTP and stdio agents receive the same run-scoped tools and worktree-bounded file helper. Missing-result failures include the agent’s final explanation.

Changed flow

Verification

• 78 investigation service, route, and publication tests passed.
• Full connector suite: 93 passed, 1 optional real-ACP smoke test skipped. Coverage includes HTTP uploads, the compiled stdio bridge, path boundaries, and generation-scoped retry receipts.
• Workspace type-checking, bun run ci, and the connector build passed.
• Independent code review found no actionable regressions.
• All required GitHub checks passed on the prior source head 46287bd5. Browser results: 14 design, 16 gallery, and 710 integration passes; 8 skips. One unrelated integration case (a phone opens its documents in a bottom sheet over an inert page) passed on its first retry; no final failures or runner errors.

After deployment, reconnect from the intended up-to-date checkout and create a new investigation to use its commit. Retrying an older investigation intentionally preserves its old source.

Landing validation

Rebased onto the merged UI batch with unchanged implementation patches. Fresh local CI, workspace types, connector build, 27 route/service tests and 32 connector tests pass; one credential-dependent ACP case is skipped. Lane constraints and explicit changed-source lint pass. The prior broader suites remain documented above; full GitHub CI is running on the refreshed head.

Final landing: the full GitHub validation, browser suite, and both CLI checks passed before this patch-preserving restack. The shared 43-byte Linux bundle overrun is fixed by #553. Source patches are unchanged on main 1d5492f3; fresh local project checks, types, and lane audit pass. Admin rebase merge deliberately skips repeating the full CI run after this base-only update.