session: own manager stop tasks

[yisding]

Problem

SessionManager kept cancellation-surviving stop tasks in a keyed dictionary, but created them with raw asyncio.create_task(). That made the bookkeeping intent implicit and left the task outside the runtime ownership model being adopted across the bug-resistant refactor.

Changes

• create keyed Session stop operations through a named RuntimeTaskScope
• retain the existing per-key force-escalation and completion-callback behavior
• assert that a stop remains strongly owned after its waiter is cancelled and leaves the scope after the force sweep settles
• reduce the reviewed raw-task-spawn inventory from 36 to 35
• document the named manager stop cohort in the production lifecycle guide

Why / impact

Cancelled API waiters no longer separate Session teardown from the repository's explicit task-ownership conventions. The existing force retry still targets the exact keyed task, while the scope now provides consistent ownership and terminal exception handling.

Root cause

The manager's keyed dictionary supplied strong references but predated RuntimeTaskScope, so the same lifecycle obligation was represented as an unclassified raw spawn.

Checks

• SessionManager and source-inventory tests outside the sandbox — 25 passed
• Ruff on changed Python files — passed
• mypy on session_manager.py — passed
• pre-commit hooks — passed
• parent stack just check — 8,580 passed / 309 skipped

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[chatgpt-codex-connector]

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