Resolve server-move source access before freezing writes

[bb-slop-cop]

🚨 SLOP COP 🚨 · new-issue-autopilot

Human comments

What was wrong

The server-move coordinator freezes public writes before obtaining the source host's Connect grant. Grant acquisition can require a POST to the account plugin, which the existing freeze middleware rejects with HTTP 503. The move then fails before handoff. Reproduced on trusted main in two clean checkouts: https://get-bb.github.io/reports/issues/4837.html

What changed

Resolve the source grant before freezing writes, honoring cancellation before entering the frozen stage. Keep the existing freeze exemptions, schedule pausing, stop-work, plugin suspension, and handoff behavior. Extend the existing Connect coordinator test to exercise account RPC availability through the real freeze middleware and a migrated SQLite database. No public protocol, authorization, dependency, or stored-data changes.

How you verified

• Added the regression before changing production code. On unchanged main, it fails with account RPC status [503] instead of [200]; the same failure repeats in a second clean checkout.

• After the fix, pnpm exec turbo run test --filter=@bb/server -- test/server-move/coordinator.test.ts -t 'source grant requires' passes.

• pnpm exec turbo run test --filter=@bb/server -- test/server-move: 97 tests pass across 16 files, including cancellation, recovery, write fences, and handoff.

• pnpm exec turbo run typecheck --filter=@bb/server, the configured formatter check, and git diff --check pass.

• Changed-line count against origin/main: 55 text lines (42 additions + 13 deletions), 2 files, no binary changes, one existing subsystem.

• Scope: coordinator/HTTP-boundary regression; no live authenticated cloud or macOS desktop run.

• Review follow-up: the regression's freeze middleware now reads coordinator.isFrozen(), the same predicate the production /api/v1/* freeze gate uses, instead of the SQLite freeze flag. Against the unfixed coordinator it still fails with [503] instead of [200], and after the fix it passes: 24 coordinator tests pass and 97 server-move tests pass across 16 files, with lint/typecheck for @bb/server green.

Fixes #4837

AGENT GENERATED