Plan 03-01 Summary: Backoff schedule and BridgePort contract

Status: done (unit-verified). No live I/O; nothing in this plan is live-gated.

Files

• src/core/backoff.ts (new): computeBackoffDelayMs(attempt, baseMs, capMs, random). Full jitter: random() * min(cap, base * 2^attempt). Imports nothing. The random source and any sleep are injected.
• src/core/ports.ts (extended): added BridgePort, BridgeEvent, and BridgeKind beside ExecutionService. The import of ErrorCode is type-only. ExecutionService lines are unchanged.
• test/core/backoff.test.ts (new): 11 tests, each title citing ANDA-03 and/or RT-04.

Verification

• npx tsc -p tsconfig.json: no errors.
• node --test dist/test/core/backoff.test.js: 11 pass, 0 fail, 0 skipped.
• npx eslint on the three owned files: no issues.

Requirement evidence

• ANDA-03: the bounded, jittered schedule is unit-tested for the Anda parameters (base 500, cap 30000). The reconnect loop itself is not in this plan; it belongs to the Anda client (plan 03-06).
• RT-04: the same schedule is unit-tested for the AgentOS parameters (base 500, cap 8000). The restart supervisor is not in this plan; it belongs to plan 03-07.

Design choices (not fixed by the plan)

• BridgePort.snapshot() returns the most recent BridgeEvent, or null before the first event. This keeps the port to one event type and matches the "current snapshot" wording without adding a second status type.
• The random source contract is [0, 1] inclusive, because the plan's test uses 1 as the upper jitter bound. The result is always at most the cap. A draw outside [0, 1] or not a number throws RangeError, so it fails closed.
• Invalid attempt, base, or cap values throw RangeError instead of returning a delay. A zero base returns 0, not NaN. A large attempt clamps at the cap.
• BridgePort.connect and close return Promise<void>, and subscribe returns an unsubscribe function. This matches D-64 and D-65.

Deviations and open items

• None against the plan's acceptance criteria.
• No dependency was added. No src/core module outside this plan was edited.