Concise switch resets to off on composer remount

[jacktrnr]

Important

Problem — The composer's Concise switch (#1633) resets to off whenever the composer remounts. Starting a chat with it on loses the setting once the first message creates the session (the new-chat composer is replaced by the session composer), and opening the Changes tab in a narrow layout unmounts and remounts the composer. Flipping it mid-chat appears to work only because nothing remounts afterwards. The switch is described as a per-session setting but is actually per-component-instance state.
Approach — Hold the flag in a small in-memory store keyed per session (server scope + directory + session id), with a draft key for the new-chat composer that is promoted to the real session key at session creation — the same moment the draft's agent/model selection is promoted today.
Scope — in: flag survives composer remounts, the new-chat → session handoff, and session switching; each session keeps its own value. · out: persistence across app reloads, a global default, any change to what the directive says or how it is sent.
Assumptions — In-memory lifetime (reset on reload) is acceptable; the existing session-creation path is the single point where a draft becomes a session.

Acceptance Criteria

• Switching Concise on in a new chat and sending the first message leaves it on in the resulting session.
• Opening and closing the Changes tab (narrow/mobile layout) does not change the switch.
• Two sessions hold independent values; switching between them restores each one's value.
• If session creation fails, the draft's value is retained for the retry.
• A session with no recorded value reads as off.

Key Decisions

• Lifetime: per session, in memory. Persisting to disk was considered and deferred — it would also need a migration story for a turn-shaping flag.
• Own store, not the model/agent selection state. That state is persisted and owns picker concerns; folding a turn-shaping flag into it couples unrelated settings and contradicts the in-memory decision.
• Lifting the signal into the session layout was rejected — it fixes the Changes-tab remount but not the new-chat → session handoff.
• Fix lands on feat(skills): concise mode — toggleable output-shaping skill #1633's branch before it merges, so the switch never ships broken.

Constraints & Invariants

• Flipping the switch still sends nothing; the directive is still read at submit time and rides as the invisible per-turn system instruction.
• Shell and slash-command turns remain unaffected.

Prior Art

• The draft → session promotion of agent/model/variant in the prompt submit path and the local selection context — mirror its keying and timing.

Source

Follow-up to #1633 · Related: #1330 (parked response-presentation epic)