## Why
`/goal` is supposed to keep Codex working until the goal is actually
done. The previous continuation logic had two ways to stop early: the
continuation prompt told the model to wait for new input when it felt
blocked, and the runtime suppressed another continuation turn after a
continuation finished without any tool calls.
That made goals stop short even when the agent could still keep making
progress (I received a few reports of this from users). It also relied
on a brittle heuristic that treated "no registry tool calls" as
equivalent to "should stop."
## What changed
- removed the continuation prompt sentence that told the model to stop
and wait for new input when it could not continue productively
- removed the goal runtime suppression heuristic that stopped
auto-continuation after a no-tool continuation turn
- deleted the continuation-activity bookkeeping and left `tool_calls` as
telemetry only
- added focused regressions for the two intended behaviors: completed
no-tool continuation turns still continue, while `request_user_input`
keeps the existing turn open instead of spawning a new continuation
Adds the core runtime behavior for active goals on top of the model
tools from PR 3.
## Why
A long-running goal should be a core runtime concern, not something
every client has to implement. Core owns the turn lifecycle, tool
completion boundaries, interruptions, resume behavior, and token usage,
so it is the right place to account progress, enforce budgets, and
decide when to continue work.
## What changed
- Centralized goal lifecycle side effects behind
`Session::goal_runtime_apply(GoalRuntimeEvent::...)`.
- Starts goal continuation turns only when the session is idle; pending
user input and mailbox work take priority.
- Accounts token and wall-clock usage at turn, tool, mutation,
interrupt, and resume boundaries; `get_thread_goal` remains read-only.
- Preserves sub-second wall-clock remainder across accounting boundaries
so long-running goals do not drift downward over time.
- Treats token budget exhaustion as a soft stop by marking the goal
`budget_limited` and injecting wrap-up steering instead of aborting the
active turn.
- Suppresses budget steering when `update_goal` marks a goal complete.
- Pauses active goals on interrupt and auto-reactivates paused goals
when a thread resumes outside plan mode.
- Suppresses repeated automatic continuation when a continuation turn
makes no tool calls.
- Added continuation and budget-limit prompt templates.
## Verification
- Added focused core coverage for continuation scheduling, accounting
boundaries, budget-limit steering, completion accounting, interrupt
pause behavior, resume auto-activation, and wall-clock remainder
accounting.
