APP-92: Bound chat execution and task history

[temp-deepshard]

Why

One-shot chat must stop when the device task settles and must not leak, invent, or silently truncate task context.

Changes

• exits on the device's final task state while keeping the timeout caller-selected
• rejects non-positive timeout and output limits before device access
• bounds output and keeps thinking and tool details opt-in
• bounds and orders task history
• rejects follow-ups to completed tasks instead of silently creating a new task

Validation

• exact pushed commit 082f79d: 181 passed
• invalid bounds fail before device resolution
• completed-task and ordered-history cases pass
• final combined suite: 216 passed, 9 subtests passed
• automated CI: none configured; validation was run manually

Base: #41

Linear: APP-92