fix(coding-agent): cap agent-level retry backoff

[junhoyeo]

The agent-level retry delay was baseDelayMs * 2 ** (attempt - 1) with no ceiling, so raising retry.maxRetries stopped being a retry policy and became an unbounded sleep. retry.provider.maxRetryDelayMs only bounds provider-requested delays, not this loop.

With maxRetries: 30 and a 1s base the schedule was:

attempt	wait	cumulative
6	32s	1.1m
10	8.5m	17m
14	2.3h	4.6h
20	6.1d	12d
30	6213d	12427d

Change

• Added retry.maxBackoffMs (default 60000, 0 disables the cap) and clamped the agent-level delay to it in _handleRetryableError.
• With the defaults plus maxRetries: 30 the delays are 2s, 4s, 8s, 16s, 32s, then 60s for each remaining attempt, about 26 minutes of retrying instead of 12427 days.
• Existing behavior is unchanged for the default maxRetries: 3 (2s, 4s, 8s all sit under the cap).

Tests

• test/suite/agent-session-retry-events.test.ts: asserts the emitted auto_retry_start delays are [1, 2, 4, 4, 4] under a cap and [1, 2, 4, 8] when the cap is disabled. Mutation-checked: reverting the clamp fails the first with [1, 2, 4, 8, 16].
• test/settings-manager.test.ts: default is 60s, explicit 0 survives, and the legacy retry.maxDelayMs migration still lands on retry.provider.maxRetryDelayMs rather than the new key.

test/settings-manager.test.ts                     39 passed
test/suite/agent-session-retry-events.test.ts     30 passed
test/suite/regressions/4491-provider-stale-after-401.test.ts,
test/suite/regressions/3317-network-connection-lost-retry.test.ts,
test/suite/agent-session-compaction.test.ts       42 passed
npm run check                                     rc=0

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.
To continue using code reviews, add credits to your account and enable them for code reviews in your settings.