fix(server): discard unread Claude steers on interrupt

A steer pushed into the live SDK query input survived query.interrupt():
the SDK dequeued it afterwards and resumed the turn the user had just
stopped. Codex clears pending turn input when it aborts a turn; Claude
does not, so its adapter now cancels the SDK messages it queued before
interrupting.

Interrupt-discards is the deliberate ceiling for steer cancellation:
Codex exposes no un-steer operation, so a cross-provider take-back
cannot exist. A steer the model never read keeps its transcript row.

docs/glossary.md

@@ -43,6 +43,7 @@ Authoritative terminology. UI label wins. Don't invent synonyms; use what's here
 - **Agent controls** — Provider, model, mode, thinking, and provider-feature controls for an agent or draft agent. Code: `AgentControls` / `DraftAgentControls` (`packages/app/src/composer/agent-controls/index.tsx`). Forbidden: "Agent status bar".
 - **Composer footer** — Optional area rendered below the composer input but still inside the keyboard-shifted composer layout. Code: `Composer.footer` (`packages/app/src/composer/index.tsx`).
 - **Composer track** — A contextual lane at the foot of a pane, by the composer input. Specific tracks use the `<thing> track` form: **Queue track**, **Subagents track**, **Tasks track**. The subagents and tasks tracks are pills floating over the transcript, each opening a panel with its rows; the queue track is a lane inside the composer itself. Code: queue track inside `Composer` (`packages/app/src/composer/index.tsx`), pill and panel frame in `packages/app/src/composer/tracks.tsx`, `SubagentsTrack` (`packages/app/src/subagents/track.tsx`), `AgentTaskList` (`packages/app/src/composer/task-list/index.tsx`).
+- **Steer** — A follow-up admitted into an agent's already-running turn instead of interrupting it. Interrupting the turn discards steers the provider has not read yet; there is no take-back short of that, and no provider offers one. The stop button and Escape both interrupt. A steer the provider never read keeps its transcript row, matching Codex. UI: "Send and steer". Code: `steerActiveTurn` (`packages/server/src/server/agent/agent-sdk-types.ts`). Don't confuse with **Queue track**, which holds messages client-side until the turn ends and never enters the running turn. Forbidden: "Delivery", "Queued prompt".
 - **Subagent** — User-facing term for an agent session related to a parent agent session. Use **subagents** in UI copy and docs. Internal daemon/provider plumbing may say "child agent" or `child_session`, especially for provider-managed imports; do not surface "child agent" as a product term.
 - **Attachment tray** — The selected-attachments row inside the composer input, above the text input. Code: `renderAttachmentTray` (`packages/app/src/composer/index.tsx`). Forbidden: "Attachment bar".
 - **Fork** — Starting a NEW agent session seeded with a copy of another session's curated chat history. The history rides along as a `chat_history` composer attachment on a draft; the fork does **not** resume or branch the provider-side session, and the source session keeps running untouched. Two targets, one surface, one RPC (`agent.fork_context`, gated on the `agentForkContext` host feature). UI: the fork menu lives in the assistant turn footer and offers "Fork in a new tab" / "Fork in a new workspace". On a **completed** turn it sits beside the copy button and pins a boundary to that turn, so the fork stops where the turn ended. On the **in-flight** turn it sits beside the progress loader and elapsed timer, and omits the boundary entirely — `selectForkContextRows` projects the whole timeline when no boundary is given, so the fork captures everything **up to now**, including the response still streaming. That omission is what makes mid-run forking work; pinning a boundary there would silently drop the live response. Forbidden on provider-subagent (read-only) panes. Code: `useForkAgent` (`packages/app/src/hooks/use-fork-agent.ts`), `selectForkContextRows` (`packages/server/src/server/agent/activity-curator.ts`). Don't confuse with: git fork (unrelated; Paseo has no such concept), **Worktree** (filesystem isolation, not history copying).

docs/providers.md

@@ -81,7 +81,9 @@ OpenCode owns user message IDs. Do not pass Paseo-generated IDs to OpenCode prom
 
 `AgentManager` owns the one canonical timeline row for a foreground prompt carrying a Paseo `clientMessageId`. It records that row when `startTurn` accepts, with the wire `messageId` set to the same value. Provider adapters still emit their native user-message echo with the same `clientMessageId` when available; the manager records its provider identity on the internal row without changing or redispatching the wire item. If an adapter emits the echo before `startTurn` resolves, the manager records the provider identity with the row at acceptance. Provider adapters continue to own externally initiated user rows that have no Paseo client identity. Do not perform global transcript text dedupe.
 
-Active-turn steering is an optional `AgentSession.steerActiveTurn` operation. The manager owns admission against its exact foreground turn, canonical user-message creation, echo reconciliation, and falls back to the normal interrupt-and-replace path only when the adapter reports `unavailable`. An adapter error is ambiguous delivery and must surface without an interrupt or retry. Codex calls `turn/steer` with the native expected turn and Paseo client user-message ID. Claude pushes an admitted steer into the exact active SDK query input; isolated control commands remain unavailable. The released OpenCode v1 adapter does not implement this operation.
+Active-turn steering is an optional `AgentSession.steerActiveTurn` operation. The manager owns admission against its exact foreground turn, canonical user-message creation, echo reconciliation, and falls back to the normal interrupt-and-replace path only when the adapter reports `unavailable`. An adapter error leaves the steer's fate ambiguous and must surface without an interrupt or retry. Codex calls `turn/steer` with the native expected turn and Paseo client user-message ID. Claude pushes an admitted steer into the exact active SDK query input; isolated control commands remain unavailable. The released OpenCode v1 adapter does not implement this operation.
+
+A steering adapter also owes its interrupt: stopping a turn must discard the steers the provider has not read yet, or one of them resumes the turn the user just stopped. Codex clears pending input when it aborts a turn; Claude does not, so its adapter cancels the SDK messages it queued before calling `query.interrupt()`.
 
 Rewind accepts the canonical wire `messageId` and resolves it to the provider identity before calling the adapter. A submitted prompt cannot be rewound until its provider echo supplies that identity.