feat(worker): make turn inactivity timeouts configurable

[andrewkcchung]

Why

Turn silence is not inherently failure: legitimate tools and models can have very different quiet periods. Making the existing worker watchdog configurable gives every deployment a common bounded mechanism for detecting genuinely stalled turns without forcing one fleet's timing assumptions on the platform.

What changed

• Add an SDK worker option for the turn inactivity timeout.
• Support deployment configuration through PILOTSWARM_TURN_INACTIVITY_TIMEOUT_MS.
• Preserve the existing timeout when no valid override is supplied.
• Let an explicit value take precedence over the environment; 0 intentionally disables the watchdog.
• Document the public configuration and edge behavior.

Behavioral proof

Command:

npm run build --workspace=packages/sdk
node --test packages/sdk/test/unit/worker-turn-inactivity-timeout.test.mjs

• Red — test-only patch on main: The test failed because main did not provide the timeout resolver or configurable worker behavior.
• Green — this branch: SDK build succeeded; 6 tests passed.

Risk assessment

Relative risk: Low

The new timeout is optional and preserves the established default when absent or invalid. It changes no durable state or wire format. The main behavioral risks are disabling protection with 0 or selecting a threshold below legitimate quiet operations; precedence, environment parsing, default, disable, and invalid-value tests cover these cases.

Review focus

• Confirm environment configuration is resolved when the worker is constructed, not dynamically during a turn.
• Confirm invalid, negative, and non-finite values retain the established default.
• Confirm 0 as the explicit disable value is an acceptable public contract.
• Review whether the documented default remains suitable across supported worker environments.