Fork an agent session mid-run from the in-flight turn footer (#2638)

* feat(app): fork an agent session mid-run from the tab menu

Forking already existed, but only on the footer of a *completed*
assistant turn. While an agent is running, the in-flight turn renders
RunningTurnFooter with no fork menu, so exploring another path meant
scrolling back to hunt for an older turn's footer — or waiting for the
run to finish.

Add two entries to the agent tab context menu ("Fork chat in a new tab",
"Fork chat in a new workspace"), reachable regardless of run state. They
omit the fork boundary, and selectForkContextRows projects the whole
timeline when no boundary is given, so a mid-run fork carries everything
up to now — including the partially streamed in-flight turn.

Fork logic moves out of agent-stream/view.tsx into a shared useForkAgent
hook so the turn footer and the tab menu share one code path; the
per-turn behavior is unchanged (it still pins a boundary to its turn).

No server, protocol, or capability changes — this reuses the existing
agent.fork_context RPC and agentForkContext host feature. The daemon
handler is already a pure in-memory timeline read, so it was safe
mid-turn before this change.

* fix(app): resolve missing agent records before failing a fork

handleForkAgent read the agent record from the session store and gave up
if it was absent from both agents and agentDetails. A persisted agent tab
can outlive its record — restored on startup before hydration — so both
fork entries failed with a generic toast even though the agent exists on
the daemon and is perfectly forkable.

Fall back to client.fetchAgent and store the result before failing,
mirroring the resolution path agent-panel.tsx already uses. Only report
forkFailed when the agent genuinely cannot be resolved; a disconnected
host now says so instead.

The resolution logic lands in resolveForkAgentSource with injected
dependencies, since workspace-screen.tsx has no handler-level test
harness and a sibling testable module is the pattern in this directory.

storeFetchedAgentDetail moves out of panels/agent-panel.tsx into
utils/agent-detail-store.ts so the workspace screen doesn't import a
panel module — and into its own file rather than agent-directory-sync.ts,
which would close an import cycle through legacy-daemon-workspaces.

* feat(app): fork from the in-flight turn instead of the tab menu

Move the mid-run fork affordance to where the fork button already lives:
the assistant turn footer, beside the progress loader.

RunningTurnFooter previously showed only a spinner and elapsed timer, so
the fork button vanished for the whole duration of a run. It now renders
AssistantForkMenu alongside them, reachable the moment a run starts.

The in-flight fork passes no boundary, so selectForkContextRows projects
the whole timeline and the fork captures the response being streamed. A
fork button sitting next to a live response that silently dropped that
response would be worse than no button. Completed turns still pin their
own boundary, enforced by a separate handler type that keeps boundary
required.

layout.ts is untouched — the affordance is added to the running footer
component rather than by lifting the footer suppression, so no copy or
duration affordance leaks onto an incomplete turn.

Reverts the workspace tab context menu approach, along with the agent
resolution helper and store-writer extraction that existed only to serve
it. The footer path already holds the agent record.

* test(app): cover the in-flight turn fork with a Playwright spec

Extends the existing assistant fork menu spec rather than adding a
sibling file, so the completed-turn and in-flight cases sit side by side.

The new test pins the behavior that defines the feature: the in-flight
fork omits the boundary fields entirely, while the completed-turn fork
sends one. Both assertions read the actual agent.fork_context frames off
the WebSocket, using the read-only page.on("websocket") idiom from
helpers/timeline-delivery.ts so the observer cannot perturb the flow it
measures. Note the request omits the fields rather than nulling them —
daemon-client spreads them conditionally — so absence is what's asserted
there, and null only on the response.

Also asserts the fork trigger is scoped inside turn-working-indicator,
that no copy or duration affordance leaks onto the incomplete turn, that
the attachment carries the streamed text, and that the source agent keeps
streaming afterwards.

* test(app): cover the in-flight fork call site, gate, and teardown

Three behaviors this PR introduced had no coverage below the Playwright
spec. A copy-paste of resolveAssistantTurnForkBoundary into
handleForkInFlightTurn would have left every unit test green.

view-fork-in-flight.test.tsx mounts the real AgentStreamView with the
render strategy stubbed to the live-auxiliary slot, so handleForkInFlightTurn,
useStableEvent and the readOnly expression all stay real. It asserts the
fork request has no boundary KEY — matching the wire contract, where the
field is absent rather than null — for both targets, and that the read-only
gate withholds the trigger, with positive controls either side so an empty
tree cannot pass for a working gate.

turn-footer.test.tsx covers the race this PR created: the fork menu now
mounts only while a run is in flight, so a fork can be pending when the
subtree is torn down. The behavior is benign — React 18 makes the orphaned
setState a no-op — so the test asserts the observable outcome and leaves a
tripwire for unhandled rejections, since AssistantForkMenu's finally has no
catch.

Each test was verified by mutation: adding boundary: undefined, dropping the
readOnly gate, and keeping the running subtree alive each fail the matching
test.

Scoped to what this PR changed. The relocated hook's error paths, draft
setup construction, and attachment metadata predate it and stay untested
here.

* test(app): replace mocked fork coverage with Playwright

---------

Co-authored-by: Mohamed Boudra <boudra.moha@gmail.com>

docs/glossary.md

@@ -40,6 +40,7 @@ Authoritative terminology. UI label wins. Don't invent synonyms; use what's here
 - **Composer track** — A contextual lane above the composer input. Specific tracks use the `<thing> track` form: **Queue track**, **Subagents track**. Code: queue track inside `Composer` (`packages/app/src/composer/index.tsx`), `SubagentsTrack` (`packages/app/src/subagents/track.tsx`).
 - **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).
 - **Conflict** — Two distinct senses; do NOT use the bare word in UI copy without qualifying which: (a) **stale-write conflict** on `paseo.json` ("Config changed on disk", code `stale_project_config`, `packages/app/src/screens/project-settings-screen.tsx:593`); (b) **git merge conflict** (no current UI string).
 - **Product discussion** — Where non-bug product talk goes: [GitHub Discussions](https://github.com/getpaseo/paseo/discussions) and `#product` in Discord. Covers workflows, features, and product direction. The container term; the ask inside it is always a **workflow** — what you're doing, how you do it today, where Paseo gets in the way. Issues are bugs only. Forbidden: "Feature request" as a Paseo surface, label, or invitation; the phrase is only used when answering someone who arrived with it. Don't invent "feature discussion", "idea", or "workflow thread" as synonyms. See [CONTRIBUTING.md](../CONTRIBUTING.md).