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).