## Problem
The `CONTEST_ACTIONS` list in `handle_command` was a manually maintained
parallel of `ACTIONS` that had already drifted (`pick` was incorrectly
included, breaking `:CP pick` cold). `navigate_problem` only cancelled
the `'run'` panel on `next`/`prev`, leaving interactive and stress
terminals alive and in-flight `run_io_view` callbacks unguarded.
`pick` and `cache` also appeared twice in tab-completion when a contest
was active.
## Solution
Replace `CONTEST_ACTIONS` with a `requires_context` field on
`ParsedCommand`,
set at each parse-site in `parse_command` so the semantics live with the
action definition. Expand `navigate_problem` to call `cancel_io_view()`
and
dispatch `cancel_interactive`/`stress.cancel` for all panel types,
mirroring
the contest-switch logic. Filter already-present `pick` and `cache` from
the
context-conditional completion candidates.
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