Graduate idle provider session reaping

[ScaleLeanChris]

What was wrong

Idle release for restorable non-Codex providers remained behind the default-off providerSessionReaping experiment added after #1604. Existing installations could also retain a persisted false value. As a result, the host daemon skipped otherwise safe release for idle Claude Code, Pi, and ACP sessions under normal settings. The reproduced root cause and alternatives are documented in issue #1604.

What changed

• Graduate idle release into standard behavior for every provider session that reports restore support.
• Preserve the legacy thread-scoped Codex fallback and apply open-turn, command, agent, workflow, and monitor protections to every provider.
• Remove the experiment setting and the server-owned /internal/runtime-policy endpoint that existed only to distribute it.
• Bump HOST_DAEMON_PROTOCOL_VERSION from 146 to 147 because older daemons still request that removed endpoint and skip non-Codex release when it is unavailable.
• Update web, mobile, desktop, database, contract, documentation, and generated-guide source fixtures that referenced the graduated experiment.

How you verified

• Added a lifecycle regression that failed before the runtime change because a restorable Claude Code session remained loaded, then passed after the change.
• pnpm exec turbo run typecheck for the nine affected packages: 12 tasks passed.
• Agent runtime lifecycle: 36 tests passed.
• Host daemon focused suite: 85 tests passed.
• Host-daemon contract: 38 tests passed.
• Web settings/layout: 9 tests passed. Server experiments: 4 tests passed. Database experiments: 1 test passed.
• Mobile full suite: 123 files and 830 tests passed.
• Templates: 41 tests passed across the local and packed external scaffold suites after building the Plugin SDK prerequisite.
• git diff --check passed and no removed experiment or runtime-policy symbols remain.
• Mobile typecheck is not included because the current package script invokes tsc, while its TypeScript 6 alias exposes tsc6; this is unchanged by this PR.

Controlling BAC work order: BAC-117

Fixes #1604

AGENT GENERATED: by GPT-5.6