feat(studio): run chats in parallel in the Chat tab (#7455)

* feat(studio): run chats in parallel in the Chat tab

New Chat used to cancel whatever the current conversation was generating.
It now leaves it running, like switching to the Train or Export tab: the
sidebar shows which chats are still going, and Stop is per conversation.

Plain `unsloth studio` launched llama-server with one decode slot, so the
admission queue serialised every chat regardless of what the UI did. Both
entry points now default to the same slot count as `unsloth studio run`.

A model swap still ends every running chat, since they all decode on one
llama-server. /load and /unload now refuse with 409 and name those chats
unless the caller passes force_cancel_active, and the UI asks first.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix(studio): scope the composer tool badge to its own conversation

The green "Running Python: ..." badge above the composer read a single
global store value, so one chat's tool call showed above every other
chat's composer, including a brand-new empty one. Its elapsed counter
also restarted at 0 on every thread switch, and a run ending anywhere
cleared the badge everywhere.

Key the status by thread and store the moment it started, so each
conversation shows only its own tool call and the counter resumes rather
than restarts. Also adds a test that every conversation gets its own
tool sandbox directory, which parallel tool calls depend on.

* Fix stalled tool calls while awaiting approval for PR #7455

Three problems, all from the approval prompt behaving as though only one
chat could ever run.

Arguments were not streamed for a gated call, so the chat stayed blank for
as long as the model took to write the payload, which for a large file is
minutes. Nothing runs before the decision either way, and the code is what
is being approved, so python and terminal now stream their card while
gated. render_html stays suppressed: its card renders the payload.

The status read "Running ..." with a climbing timer while the call had not
started. It now reports that it is waiting for approval, then switches to
running once allowed.

The admission lease was held across the wait, so four unanswered prompts
held all four decode slots and no other chat could start while llama-server
sat idle. A parked run keeps its lease but no longer counts against
capacity.

Measured with four prompts left open: every gated call streamed its code,
none reported running, and a fresh chat answered in 0.4s where it
previously waited 290s and never did.

* Fix duplicated and truncated tool cards for PR #7455

A gated tool call rendered two cards: the provisional one that streams the
arguments, plus a second one keyed by the approval id. Only the second ever
got its tool_end, so the first spun "Running" for the rest of the chat.
Reuse the open part when the approval prompt arrives.

The terminal card also showed nothing but a 60-char trigger label, so a long
heredoc read as no progress at all. It now renders the command the same way
the Python card renders its script, and neither is capped at 10k chars.

Both cells moved inside the collapsible, so one chevron hides the code with
the output and Copy / Download exist only while the card is open. A card
parked on the prompt says so instead of counting up "Running".

* Fix review findings on the parallel-chat gate for PR #7455

Backend:
- /unload rechecks active generations under the lifecycle gate, like /load,
  and lets its 409 through the catch-all instead of rewriting it as a 500.
- /load gates only once _load_model_impl has decided this is a real reload,
  so an Apply on the already-loaded model no longer refuses, and the retry it
  asks for no longer cancels every chat before returning already_loaded.
- The direct /v1/responses stream registers in the cancel registry, so a
  non-forced unload can no longer tear llama-server down under it.
- run_server defaults to the same slot count as the CLI. colab.py calls it
  without the argument, so Colab was still serialising every chat.

Frontend:
- Cancelling a backgrounded chat aborts its own request rather than only
  posting a cancel id, which is the only thing that ends an external-provider
  or audio run.
- The model-swap dialog counts local runs only, and falls back to the backend
  when this tab's map is empty, so a reload or a second tab still gets asked.
- Context usage and the diffusion canvas are scoped to the chat that produced
  them; a compare row reads activity from its member threads.

Tests:
- The extracted-source cancel harnesses supply the active-generations module,
  which the tracked-cancel class now depends on.

* Fix the swap confirmation scope and cancel timing for PR #7455

A forced load cancelled every chat before the model identifier, GPU selection,
training coexistence and download checks had run, so a load that then failed
those checks stopped the chats and replaced nothing. The refusal still happens
early, but the destructive cancel now sits immediately before the teardown it
is paying for, and rechecks under the gate like /unload does.

The swap dialog only reconciled with the backend when this tab looked idle, so
one local chat was enough to hide a second tab's runs. Confirming then sent
force_cancel_active, which cancels every backend run, including the ones the
dialog never mentioned. The backend snapshot is now merged in every time, so
the dialog names what will actually stop. External-provider runs are never
registered there, so the union stays local-only.

Also drops the active-generations docstring claim about restoring sidebar
spinners, which nothing consumes.

* Defer destructive cancels and track every local stream for PR #7455

/unload cancelled the running chats before it had resolved that it unloads
anything. A stale model_path, which a second tab produces routinely, killed
every chat and then no-opped, leaving the resident model up. It now refuses
early and cancels only at each teardown, matching /load.

The swap dialog also stopped every chat locally the moment the user confirmed,
which threw away the two-phase backend behaviour: a load that then failed
identifier resolution, GPU validation or the training guard had already
truncated the replies. The backend now owns the cancel.

Three local streams decoded on llama-server without registering, so a
non-forced unload counted zero generations and tore the server down mid
response: /v1/completions streaming, and the plain and server-tool Anthropic
streams, the first of which is the default /v1/messages path. Note this makes
a non-forced load return 409 during those runs rather than draining quietly,
the same trade the /v1/responses fix made.

The safetensors tool loop still announced a gated call as running while it
waited on a human; only the GGUF loop had been fixed. A source-level parity
test now pins both.

Also drops stopAllChatThreads, which has no callers left.

* Studio: close three load/unload gate races found in review

Re-check the in-flight load guard after the stop-running-chats confirm.
The confirm always GETs active-generations before its zero-running
early-out, so the guard no longer sits atomically ahead of the
reservation and two picks in that window both reached performLoad over
the same refs. ejectModel had the same shape and gets the same re-check.

Reject a sidecar swap immediately before the forced cancel in both load
branches. The previous check was back at the top of preflight, so an
install reserving during identifier resolution, the tier probe, the
training guard or the download check made the post-drain recheck 409 a
load whose chats had already been stopped.

Enter the Anthropic passthrough's cancel tracker inside its body
generator. It was entered eagerly and returned through
_sse_streaming_response, which sets no unstarted_cleanup, so a response
whose body never started left the run registered forever and 409'd every
later non-forced load and unload.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Trim comments across the files this PR touches

Tightens the comments and doc blocks in the backend, CLI, tests and frontend
files changed by this PR: collapses multi-line explanations to a single line
where they still read clearly, and drops the ones the code already says.

No code changes, verified by an AST comparison against the previous commit.

* Studio: defer the destructive cancel and close two gate gaps

Move the forced cancel behind every check that can still reject a swap.
The drain now runs first with the runs it is about to cancel discounted,
so it waits only for inference the cancel cannot end, then the sidecar
check decides, then the cancel fires, then a second drain lets those runs
unwind before teardown. A sidecar install reserving during the drain no
longer 409s a load whose chats have already been stopped.

Track the non-streaming /v1/completions proxy. It was the last local
decode path missing from active_generations, so an unload, which runs no
drain, tore llama-server down under it and force_cancel_active could not
signal it. It now uses the same tracked cancel event and dedicated client
as the OpenAI pass-through.

Skip the client's preliminary unload while chats are generating and let
/load evict at its own post-preflight point instead. Forwarding
force_cancel_active there truncated replies before identifier
resolution, the GPU and training guards and the download check had run.

Keep per-thread context usage so returning to a chat whose background run
finished restores its bar instead of leaving it blank until the next turn.

Make the running-flag clear run-specific. Every run without a resolved
thread id shares the "__default" key, so concurrent compare panes could
clear each other's flag and strand a live stop handle.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: register the embeddings proxy with the swap gate

/v1/embeddings proxied straight through the pooled client with no tracked
cancel event, so it never appeared in active_generations. /unload runs no
idle drain, so a concurrent non-forced unload counted zero generations and
killed llama-server mid-request, and force_cancel_active had no event to
signal. Mirrors the completions proxy: tracked event, dedicated unpooled
client closed by a cancel/disconnect watcher, unregister in a nested
finally so a close failure cannot leave a phantom generation behind.

* Trim comments on the newest changes in this PR

Comments only, no code changes: shorten the ones added by the load-gate
ordering, embeddings and per-thread usage work down to the same density as
the rest of the diff.

* Studio: register the legacy generate stream with the swap gate

/generate/stream built a cancel event but never entered the tracker, so it
was invisible to active_generations. Being in the keep-warm middleware's
inference suffixes only covers /load, which drains; /unload does not, so a
non-forced unload passed the 409 gate and then blocked on the standard
backend's generation lock, and a forced swap had no event to signal.
Registered inside the body generator under a nested finally so a teardown
failure cannot skip the unregister.

The AST contract test asserted the cleanup finally by overwriting its flag
per Try node, so a nested try made the last one win. Accumulate instead,
which is what the existence claim meant.

* Studio: three more swap-gate gaps found in review

Register /audio/generate with the gate. TTS holds the model for the whole
request and /unload runs no drain, so unregistered a non-forced swap counted
zero generations and tore the model down mid-generation; the orchestrator
path only waits 15s for the generation lock, which real TTS exceeds. No
cancel keys: no backend takes a cancel_event for audio, so the event has no
observer and a forced swap still cannot interrupt audio already in flight.

Thread the tracked cancel event into the /v1/responses admission wait. It
was the only admission caller passing None, so a queued run could not be
reached by cancel_all() and a plain /inference/cancel could not stop it at
all. Same omission fixed at the upstream send there and on /v1/completions.

Let an unforced unload of a stale model path reach the no-op check. Before
this PR that request returned 200 and did nothing; the new gate refused it
with 409 for a request that reaches no teardown branch. Gate both refusal
passes on the disjunction of the route's own teardown conditions, including
not is_loaded, so a mid-load GGUF still refuses.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: register the remaining non-streaming decode paths

stream defaults to false on all three of these, so they are the ordinary
shape of their routes, and each holds a local backend for the whole
request. /unload runs no idle drain, so with no registry entry a non-forced
swap counted zero generations and tore the backend down mid-request instead
of returning 409, and a forced one had no event to signal.

Non-streaming /v1/messages: all three helpers ran with an empty registry,
since only the streaming siblings were tracked. Registered at the call site
because the pass-through takes no cancel_event of its own, and with no
cancel keys, matching those siblings.

Non-streaming standard chat and audio-input chat: the trackers in this route
sit inside their `if payload.stream:` arms, so neither else branch was
covered. The GGUF sibling already registers its own non-streaming branch.

Each exit is in a finally on the branch's existing try, so the except arms
are covered too: a leaked entry 409s every later swap until restart.

* Studio: tighten the swap-gate comments

Comment-only pass over the newest swap-gate registrations: collapse the multi-line rationales in /unload, the legacy generate stream, audio generation and the non-streaming chat branches, and the matching test preambles, to the shortest form that still carries the reason. No code changes.

* Studio: stop the reselect dialog promising a stop that never happens

Picking an external provider leaves the local model resident and stops the
status poll mirroring it, so reselecting that model showed the stop-chats
dialog, and /load then answered already_loaded ahead of its cancel hook.
Confirmed with the live backend: the same pick with force_cancel_active set
still returned already_loaded and the chat kept streaming. Not stopping
those chats is right, since the load never interrupts them, so remove the
prompt rather than honour it. Blanket-skipping is unsafe, because the same
id and variant with one sampling setting changed is a real reload and 409s,
so the branch only fires when a status fetch confirms the resident
checkpoint and variant match, and then adopts it without calling /load.

Redact native model paths from the active-generations response. Registering
/generate/stream recorded backend.active_model_name verbatim, which is an
absolute path for a native local model, and this route is the only place
that serialises it. Redacting at the response covers every tracker rather
than the one that surfaced it.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: keep hydrated context usage in the per-thread map

The history loader restores a saved conversation's usage through
setContextUsage only, and it runs once per mount, so switching away and
back left the bar blank for a hydrated chat even after the per-thread map
landed. setContextUsage now writes the value through to the visible
thread's own entry and clears that entry when passed null, which covers
both hydration call sites and any future writer.

* Studio: unblock load cancellation and share unresolved thread keys

Run the two stop-loading fast paths ahead of the unload route's pre-gate
refusal. _unload_may_evict returns True for exactly the model being
cancelled, so the refusal was blocking the branch that cancels a load which
has replaced nothing and can interrupt no chat. The client made that
unrecoverable: cancelLoading sends the unload without force, drops the
result, and its abort never reaches /load, which takes no signal, so the
load ran on and could later cancel those chats and swap the model. Nothing
else is exempted; an unload that would tear down a serving model matches
neither fast path and still 409s. The comment claiming the client lets that
409 surface is corrected, since it discards it.

Hold every owner behind a shared thread key. Runs with no resolved thread id
share "__default" (concurrent compare panes, since startCompare clears
activeThreadId), so a single owner slot let a second run replace the first's
token and then delete the shared entry while it was still generating, and
the server-cancel map lost the older handle the same way. Both now hold a
list, the running and local flags survive until the last owner clears, and
stopChatThread stops every handle under the key.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: carry a confirmed swap into the sidecar install, key restored usage by thread

Picking a model that needs a newer transformers while chats generate raised the
"stop N chats" prompt, but the answer never reached the install that runs before
the load: /install-latest-transformers refused on those same chats and took no
force flag, so Retry hit the same 409 and nothing in the flow stopped them.

Carry force_cancel_active through the consent dialog into the installer. Only
the pre-gate fast path is skipped: the recheck under the lifecycle gate still
has to pass, so an unconfirmed caller is refused as before. The cancel runs last
inside the gate, after every check that can still reject the install, and the
drain behind it is bounded since it holds the gate and the sidecar reservation.

Also key restored context usage by the thread the loader read. history.load()
captures remoteId before two awaited round trips, so a switch inside that window
filed one thread's usage under another and setActiveThreadId kept re-applying it.

Preserve sibling owners when a run key is cleared without an owner: the image
rejection gate now uses its own token, and the reducer leaves owned runs alone.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: bound the post-cancel drains, and make cancellation reach the paths that ignored it

A forced swap cancels the chats it interrupts, then waits for them to unwind.
That wait had no deadline while holding the lifecycle gate, and TTS on the
subprocess backend observes no cancel event at all, so one audio generation
could pin every load, unload and new request for its whole duration. Bound both
post-cancel drains. Pre-cancel drains stay unbounded: the swap can still be
refused there, so shortening them would weaken what they protect.

/unload had the opposite problem and no drain at all, cancelling and tearing
down on the next line, which turned a clean stream end into a dropped
connection. Give it the same bounded wait, gated on the cancel having cancelled
something so an idle Eject pays nothing.

Make the cancel actually land where it can. GGUF TTS now takes a cancel_event
and a watcher closes its client to break the blocking POST. The Anthropic
non-streaming pass-through did the same thing the completions and embeddings
paths used to: register with the gate, then run both POSTs on the pooled client
that cannot be closed. It now uses a per-request client like they do.

Also: park and unpark the admission queue the reservation actually holds, since
queues are keyed by base_url and a reload mints a new port; key tool output by
remoteId on both sides, so the first turn of a New Chat stops writing under one
key and reading another; and give tool status a run owner, so a finishing run
cannot blank the badge a concurrent one is still showing.

Clamp --parallel to 1 on a llama-server without --kv-unified. The new default of
4 would otherwise split -c four ways on such a build, quartering the context
window for a feature it cannot serve.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: scope a chat's Stop to its own generation, and clear the way before a confirmed install

Safetensors generation is serialized on _gen_lock and the worker has a single
cancel event, so a chat still queued on that lock owns no generation. Its Stop
handler called reset_generation_state() anyway, which set the shared event and
ended whichever conversation was actually running. Parallel chats is what makes
that reachable.

_generate_inner now records its cancel_event as the current holder once it takes
the lock, and reset_generation_state drops a reset from anyone else. Every route
call site passes its own request event. A reset with no event stays global, so
unload and model switch cannot leave a generation alive, and a reset while
nothing runs still resets, so an error path before generation is not a no-op.
The other two backends take the argument too, or the standard one raises
TypeError on every cancel.

The sidecar install had the mirror of the /load ordering problem: it cancelled
the chats first and drained second, so an unrelated counted request the cancel
cannot reach (a count_tokens, say) was still there for the recheck, which then
refused an install that had already stopped every chat for nothing. Drain the
unreachable remainder first, discounting the registered chats, then cancel.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: close the windows the previous round's fixes left open

Three follow-ups, two of them holes in the fixes just before them.

The worker claim went in after _send_cmd, so the command was already running
unclaimed and a queued chat's Stop in that window still reset it. Claim first,
with the send inside the same try, so a failed send releases it too.

Tool status kept one entry per key with an owner. That stops a foreign clear but
not an overwrite: under the shared unresolved-thread key the second run replaced
the first's entry, and its own clear then removed the only one while the first
tool was still running. Keep per-run entries and render the newest.

/unload gated its drain on having cancelled something, so a request that passed
the keep-warm middleware but had not reached its tracker yet was invisible to it
and the teardown landed on an already-admitted request. Drain on the middleware
count instead, which covers that window as well as the cancelled runs, then
re-cancel whatever registered while waiting. Bounded, not a refusal: an unload is
deliberate, and on expiry it proceeds exactly as before.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Trim the parallel-chats comments to their reasons

Compress the multi-line rationales added by this branch into shorter forms and drop
restatements of the code below them. The reasons behind the drain bounds, the deferred
cancel, the per-request generation ownership and the thread-scoped tool and usage keys
are kept, just said in fewer lines.

* Studio: own the worker per generation, and make a resumed chat requeue for its slot

Ownership was a single lock holder, so dispatched runs (compare mode bypasses
_gen_lock by design) never claimed it and the guard fell straight through to the
global reset: a Stop on one of them ended its siblings. Track the generations
actually running instead, claimed before the send and released in the same
finally on both paths. A reset still proceeds when nothing is running, so an
error path ahead of generation is not swallowed.

park() hands the freed slot to a waiter, so a chat resuming from a tool approval
could take it back while that waiter was still decoding, putting two holders on
a one-slot server and sending the resumed tool loop past the admission limit.
unpark_async waits for room; the plain unpark stays for a holder tearing down,
which will not decode again.

Audio only observed its cancel event on a forced swap. An explicit Stop just
aborts the fetch, and this route has no cancel id, so llama-server ran on to the
request timeout after the chat reported it stopped. Watch the disconnect.

Also read tool status by remoteId, matching the key the adapter writes and the
fix already made for tool output, and stop an unresolved run from writing its
usage into whichever conversation the user moved to.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: let only the generation the worker is running speak for it, and hold a slot for a resuming chat

The ownership list recorded admission, but the subprocess runs generations one
at a time, so a dispatched request queued behind another counted as an owner and
its Stop signalled the shared cancel event, ending the request that was actually
running. Keep admission for release bookkeeping and gate ownership on execution
instead, promoted when the worker first answers that request. Nothing executing
still permits a reset, so an error path ahead of generation is not swallowed.

The worker has one cancel event and no per-request cancellation, so this decides
who may pull the lever rather than making the lever per-request.

A resuming chat also polled for a slot it could never see: release() grants to
the next waiter under the same lock, so later arrivals overtook an approved chat
indefinitely. A pending unpark now reserves the next slot and they queue behind
it.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: cover the prefill window, and keep a first turn's tool output readable

Gating worker ownership on execution left the interval between the send and the
first response uncovered: nothing is executing then, and the empty case admitted
anyone, so a queued chat's Stop still ended the one in prefill. Split the empty
case. Nothing claimed at all still permits a reset, so an error path ahead of
generation is not swallowed; claimed but unanswered resolves to the oldest
claim, which is what a FIFO command queue is working on.

Putting both sides of the tool-output scope on remoteId left the first turn of a
New Chat writing under the unresolved scope for its whole life while the readers
recomputed the moment the autosave assigned an id, so the card blanked mid-run.
The readers now fall back to the unresolved scope, which only an unpersisted
first turn can occupy.

* Studio: order the parked approvals, and tie a worker claim to its enqueue

The reservation added for admission fairness was a bare count, so every approved
holder counted against every other: park two chats, approve both, and once the
last decoder released, nothing could ever satisfy the check again. That is a
deadlock where the problem it fixed was only unfairness. Make it a FIFO ticket
so a pending unpark blocks the ones behind it and no others.

_owns_worker reads claim order to decide which request the worker is prefilling,
which only holds if claiming and enqueuing cannot interleave. Hold one lock
across both on the dispatched and the locked path.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: follow a first turn's run when its thread gets an id, and key the denoising canvas per chat

A run started before its thread existed filed every handle under "__default". Nothing
moved them once autosave assigned the real id, so the sidebar row showed no spinner and
Stop could not reach the generation, which kept holding a slot.

adoptDefaultThreadRun re-keys the run maps onto the real id from the thread adapter's
initialize(), where the id first exists; anything already filed under that id wins, since
that is a later run. The adapter captures its key once at run start, so it now resolves
the live key per use through runKeyForOwner, looking its own serverCancel up in the owner
map. Without that the migrated entries are stranded and the spinner never clears.

The denoising canvas was one global slot, so two diffusion chats overwrote each other and
the ownership tag then hid the visible preview until that thread emitted again. It is now
activeDiffusionCanvasByThreadId, written and cleared per thread, and the frame no longer
carries a threadId of its own. The bubble reads threadListItem.remoteId, dropping the dead
threadListItem.id arm: the writer tags unstable_threadId, which is exactly remoteId.

Two existing backend tests needed the same treatment. _bare_orchestrator skips __init__, so
it now sets the claim bookkeeping the worker ownership check reads. The Anthropic
passthrough gate test anchored on comment prose that a rewrap had broken; it anchors on the
code instead.

* Studio: hand the worker over cleanly between generations, and stop unresolved runs sharing each other's state

Worker ownership moved off the consumer and onto the dispatcher. Consumers read their
mailbox whenever they get around to it, so a request whose gen_done had been routed still
owned the worker while the next one ran, and a late Stop for it cancelled that one. The
dispatcher is the only place responses arrive in the order the worker produced them: it
now retires a request at its terminal response and promotes the next one, and answering a
request makes it the sole executor, since the subprocess runs one generation at a time.

reserve()'s immediate path ignored the unpark tickets that _grant_waiters_locked already
honours, so a request arriving between a slot freeing and an approved chat's next poll
took it, repeatedly. It applies the same reservation now.

Three places let concurrent first turns share state through the "__default" key. Nothing
links a run filed there to the id its thread later receives, so rather than guess, each
now declines when the key is ambiguous: adoption only re-keys a lone run, the composer
badge only claims a lone status, and the tool-output fallback only applies to a thread
that is still running. That leaves two concurrent first turns where they were before
adoption existed instead of handing one thread the other's handles.

A first turn's usage was never filed, because its key stayed null for the whole run while
autosave moved activeThreadId to the real id, so the context bar went blank after the
first reply. It resolves the adopted key like the cleanup handles do.

Cancelling a forced load left the UI with no model: the previous one stays resident until
/load's teardown, and the cancel path cleared the checkpoint without rolling back. It now
resyncs from the backend, which is right whether or not the load got that far.

The sidecar install drain is weighted 1:4 rather than halved, total unchanged. Only the
second half benefits from patience, and cutting it short refused installs whose chats had
already been stopped for nothing.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: give a first turn its real thread id before the run starts

A first turn filed every run handle under a shared unresolved key because
assistant-ui binds unstable_threadId before the thread is persisted. Two of them
overlapping there is unresolvable afterwards, and the last round's migration could
only decline rather than guess, which left neither sidebar row showing its run.

The id is available earlier than I claimed. append() already tracks
threadListItem.initialize() by the user message id, and createPersistedRunAdapter
already awaits that promise before invoking the adapter, so the thread is persisted
by the time the run begins. It was only being discarded: the tracked promise resolved
to void. It now resolves to the assigned id, and the wrapper hands it to the adapter
when assistant-ui had none. An id that is already set is never replaced, since that
would move a running chat's handles out from under the row watching them. The
existing unresolved-key guards stay as a safety net but should no longer carry weight.

The sidebar counted running thread ids rather than rows, so one compare conversation
read as two chats. It folds ids into rows through the same threadIds the row spinner
uses, and still counts a running id that matches no row.

_TrackedCancel always registered kind="chat", so an embeddings or raw completions
request appeared in the model-swap prompt as an unnamed conversation and confirming
cancelled it while calling it a chat. The non-conversation routes now pass their own
kind, and the prompt says "requests" whenever the snapshot is not all chats.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: withhold the shared worker cancel from a request the worker has left

Moving ownership to the dispatcher fixed reset_generation_state, but the token loop
signals the shared worker event directly and did not carry the same rule. A dispatched
consumer runs with mark_started off and can still be draining tokens buffered before
its gen_done was routed, so stopping it there ended whichever request the worker had
started next.

It now signals only when _owns_worker agrees, the same predicate reset_generation_state
uses. The local drain and return are unconditional, since those touch nothing but this
stream. The remaining _cancel_generation callers are deliberately global: subprocess
shutdown, the pre-load kill and unload_model.

* Studio: add the AGPL-3.0 header to the first-turn identity test

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: stop the dispatcher and a _gen_lock stream fighting over the response queue

Nothing stopped the dispatcher starting under a _gen_lock generation, so once compare
was opened while an ordinary chat was still streaming, both consumed _resp_queue and
whichever response the dispatcher took without a mailbox was dropped, gen_done included.
That chat truncated or hung. This PR is what makes it reachable, since navigating into
compare no longer ends the chat behind it.

Delaying the dispatcher would serialise compare behind whatever chat happens to be
streaming, so the direct readers get a mailbox instead. _direct_reader returns a reader,
a cancel drain and a release, and files the mailbox under _direct_mailboxes rather than
_mailboxes, which means "compare requests are in flight" to the unload and distributed
paths and must not count an ordinary chat.

Both directions close. The dispatcher finds the direct reader's mailbox instead of
dropping. And this reader can already be blocked on the queue when a compare request's
dispatcher starts, so a response that is not ours goes to its own mailbox rather than
being consumed, which would have corrupted the chat and hung the pane. All three
_gen_lock readers use it, and the cancel drain goes through it too.

The sidebar's return target still picked a raw pane id while the count grouped by row,
and /chat addresses compare with `compare`, not `thread`. It resolves through the same
items now, so a running compare row returns to its pair.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: keep worker ownership honest across audio, API traffic and a replaced worker

The audio-input send got a mailbox last round but stayed unclaimed, so a compare request
queued behind it looked like the oldest owner and stopping that queued request signalled
the shared event into the audio chat. It claims under the send lock and releases in the
finally, like _generate_inner.

Ownership is keyed on cancel-event identity with nothing tying it to a worker generation,
so a consumer still blocked on its mailbox when the process was replaced stayed recorded
as the executor, and a generation on the fresh worker could not be stopped.
_shutdown_subprocess clears that state once the process is confirmed dead, mailboxes
included: nothing routes to them again, and a stale one reads as compare activity to the
unload path. Not on the survived-SIGKILL path, which keeps its handle on purpose.

The four public /v1/messages trackers were registering as chats. The distinction is a
Studio thread, not the protocol, and those branches already say "No thread_id: public API
surface" while the Studio path passes payload.thread_id separately. They carry their own
kind now, so the swap prompt stops calling an external request a chat.

The swap confirmation still counted raw pane ids, so a compare conversation asked to stop
two chats and listed its title twice. It folds panes onto pairId and lowers the count by
what it collapsed, leaving a first turn the backend can count but not name.

Deep Research set runningByThreadId but registered no server-cancel handle, and that map
is how Stop, archive and delete reach a thread that is no longer active. Leaving the
outgoing thread running is this PR's doing, so the run was left unreachable while its
supervisor kept working against a conversation the user could delete.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: tighten the parallel-chats comments

* Studio: replay a Deep Research stop that arrived before the run existed

The handle is registered before createResearchRun resolves because the thread can be
stopped while that request is in flight, but it had no id to act on and dropped the stop.
The supervisor then followed a run the user had already stopped, archived or deleted.

It latches instead: a stop with no id yet sets a flag, and the adapter replays it against
the id the moment creation returns rather than starting to follow.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: fix worker ownership on a raced reroute, and the stop-chats prompt

Four review findings on the parallel-chats work, all reproduced first.

- _direct_reader hands a foreign response to its own mailbox, but skipped the
  ownership move the dispatcher makes. A _gen_lock reader already blocked on
  resp_queue can beat the compare dispatcher to that request's first response,
  and the compare consumer opts out of marking, so nothing promoted it: the
  direct request stayed the recorded executor, its late reset cancelled the
  compare generation, and the compare chat's own Stop was ignored.
- A chat stopped while queued on _gen_lock was still claimed and sent once the
  lock freed. Cancellation is only checked on a token, so a long prefill, or a
  generation reaching gen_done without one, occupied the worker after Stop.
  Same hole in the audio-input path, which shares the lock.
- The stop-chats prompt counted generation handles, not conversations. One chat
  holds several while a tool continuation registers its next leg before the
  previous unwinds, so it offered to stop two chats and listed one title.
- Ejecting a model confirms through that dialog, which told the user
  "Unloading the model reloads the model" and offered "Stop and reload".
  Confirming calls /unload and leaves nothing loaded.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Studio: name the TTS run's thread so the stop prompt counts it once

The audio branch registers its run locally under the thread key but sent no
thread_id, so the backend tracker filed the same generation under no thread.
The stop-chats prompt then had a named local run and an unnamed backend one and,
since e8e7594 started adding unnamed entries to the named ones, counted a single
TTS chat as two requests. The backend already reads payload.thread_id, so
sending it lines both registries up on the same run.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tests/studio/test_cancel_atomicity.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import ast
+import importlib.util
 import random
 import threading
 from pathlib import Path
@@ -107,6 +108,20 @@ _WANTED = {
 }
 
 
+def _load_active_generations():
+    """The real registry `_TrackedCancel` records runs in.
+
+    Loaded straight off disk rather than imported, so the extracted class runs
+    against the genuine module without pulling in the whole route package (and
+    without putting studio/backend on sys.path for the rest of the session).
+    """
+    path = SOURCE_PATH.parents[1] / "state" / "active_generations.py"
+    spec = importlib.util.spec_from_file_location("studio_active_generations", path)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
 def _load_registry_module():
     chunks = []
     for n in _TREE.body:
@@ -125,7 +140,7 @@ def _load_registry_module():
             and n.target.id in _WANTED
         ):
             chunks.append(seg)
-    mod = {}
+    mod = {"active_generations": _load_active_generations()}
     exec(
         "import threading, time\nfrom typing import Optional\n" + "\n\n".join(chunks),
         mod,

tests/studio/test_deep_research_frontend_contract.py

@@ -60,7 +60,9 @@ def test_research_mode_is_single_chat_and_detaches_without_cancel() -> None:
     assert 'update.event?.event === "reasoning.updated"' in adapter
     assert "The activity store coalesces these high-frequency events" in adapter
     assert '{ type: "text" as const, text: report }' in adapter
-    assert "if (abortSignal.aborted) return" in adapter
+    # runSignal, not abortSignal: each run gets its own controller, forwarded from the thread
+    # signal, so one chat's Stop cannot abort a sibling streaming in the background.
+    assert "if (runSignal.aborted) return" in adapter
     assert "await autoLoadSmallestModel()" in adapter
     assert "signal: researchFollowController.signal" in adapter
     assert "beginExternalResearchFollow(" in adapter

tests/studio/test_first_turn_thread_identity.py

@@ -0,0 +1,76 @@
+# SPDX-License-Identifier: AGPL-3.0-only
+# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0
+
+"""A first turn must reach the model adapter with its real thread id.
+
+assistant-ui binds `unstable_threadId` before the thread is persisted, so a first
+turn used to file every run handle under the shared "__default" key. Two of them
+overlapping there is unresolvable after the fact: nothing links a run under that
+key to the id its thread later receives, so the sidebar showed no spinner and Stop
+could not reach either generation.
+
+The link exists earlier. `append()` tracks `threadListItem.initialize()` by the
+user message id, and `createPersistedRunAdapter` already awaits that promise before
+invoking the adapter, so the id is known by the time the run starts. These tests pin
+that the resolved id is carried through rather than discarded.
+"""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+
+WORKSPACE = Path(__file__).resolve().parents[2]
+PROVIDER = (WORKSPACE / "studio/frontend/src/features/chat/runtime-provider.tsx").read_text(
+    encoding = "utf-8"
+)
+
+
+def test_the_tracked_promise_carries_the_assigned_thread_id():
+    # Resolving to void threw the id away, which is what forced the "__default" detour.
+    assert "Promise<string | undefined>\n>();" in PROVIDER
+    assert re.search(
+        r"trackRunStartReady\(\s*message\.id,\s*initializeThread\.then\(\(\{ remoteId \}\) => remoteId\),",
+        PROVIDER,
+    ), "append() must track the promise that resolves to the persisted thread id"
+
+
+def test_wait_for_run_start_returns_the_id():
+    assert re.search(
+        r"async function waitForRunStartHistoryAppend\([^)]*\): Promise<string \| undefined>",
+        PROVIDER,
+        re.S,
+    ), "the awaiter must hand back the id it waited for"
+    assert "return adoptedThreadId;" in PROVIDER
+
+
+def test_the_run_is_given_its_real_thread_id():
+    # The whole point: the adapter must not start under the unresolved key when the id is
+    # already known by the time the await above resolves.
+    block = re.search(
+        r"async \*run\(options\) \{.*?const result = adapter\.run\(.*?\);",
+        PROVIDER,
+        re.S,
+    )
+    assert block, "createPersistedRunAdapter's run wrapper not found"
+    body = block.group(0)
+    assert "const adoptedThreadId = await waitForRunStartHistoryAppend(" in body
+    assert (
+        "!options.unstable_threadId && adoptedThreadId" in body
+    ), "only fill in the id when assistant-ui had none"
+    assert "unstable_threadId: adoptedThreadId" in body
+
+
+def test_an_existing_thread_id_is_never_overwritten():
+    # A resolved thread already streams under its own id; replacing it would move a running
+    # chat's handles out from under the sidebar row watching them.
+    block = re.search(
+        r"const result = adapter\.run\((.*?)\);",
+        PROVIDER,
+        re.S,
+    )
+    assert block
+    arg = block.group(1)
+    assert "? { ...options, unstable_threadId: adoptedThreadId }" in arg
+    assert ": options" in arg

tests/studio/test_stop_running_chats_prompt_contract.py

@@ -0,0 +1,63 @@
+# SPDX-License-Identifier: AGPL-3.0-only
+# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0
+
+"""Source contracts for the "stop running chats" confirmation.
+
+The dialog is what a user reads before losing in-flight work, so two things have
+to hold: it counts conversations rather than generation handles, and it describes
+what confirming actually does. There is no frontend test runner in this repo, so
+these read the source the way the other frontend contracts here do.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+WORKDIR = Path(__file__).resolve().parents[2]
+FRONTEND = WORKDIR / "studio" / "frontend" / "src"
+
+
+def _read(rel: str) -> str:
+    path = FRONTEND / rel
+    assert path.exists(), f"missing source file: {path}"
+    return path.read_text(encoding = "utf-8")
+
+
+def test_the_prompt_counts_conversations_not_generation_handles():
+    # One chat holds several handles while a tool continuation registers its next leg
+    # before the previous unwinds (active_generations.ActiveGeneration mints one per
+    # __enter__), so active.count exceeds the deduplicated thread_ids and the dialog
+    # offered to stop two chats while listing one title.
+    src = _read("features/chat/utils/confirm-stop-running-chats.ts")
+    assert "entry.thread_id" in src, "the unnamed entries have to be counted separately"
+    # The raw handle count survives only for a backend too old to send the entries.
+    primary = src.index("running.length + unnamed")
+    fallback = src.index("Math.max(active.count")
+    assert primary < fallback, "the handle count must be the fallback, not the primary"
+
+
+def test_an_unload_is_not_described_as_a_reload():
+    # ejectModel confirms through the same dialog, but confirming calls /unload and
+    # leaves no model loaded: "Unloading the model reloads the model" and "Stop and
+    # reload" promised the opposite for the destructive one.
+    dialog = _read("features/chat/components/stop-running-chats-dialog.tsx")
+    assert "Stop and unload" in dialog and "Stop and reload" in dialog
+    assert "leaves no model loaded" in dialog
+
+    runtime = _read("features/chat/hooks/use-chat-model-runtime.ts")
+    eject = runtime.index('"Unloading the model"')
+    assert (
+        '"unload"' in runtime[eject : eject + 120]
+    ), "the eject path must ask for the unload wording"
+
+
+def test_the_tts_request_names_its_thread():
+    # The audio branch registers its run locally under the thread key, and the backend
+    # tracker reads payload.thread_id. Omitting it filed the backend entry under no
+    # thread, so the prompt counted the named local run and the unnamed backend one as
+    # two requests for a single TTS chat.
+    src = _read("features/chat/api/chat-adapter.ts")
+    call = src.index("const result = await generateAudio(")
+    assert (
+        "thread_id: resolvedThreadId" in src[call : call + 600]
+    ), "the TTS payload must carry the resolved thread id"

tests/studio/test_stream_cancel_registration_timing.py

@@ -10,6 +10,7 @@ from __future__ import annotations
 
 import ast
 import asyncio
+import importlib.util
 import json
 import threading
 import time
@@ -256,6 +257,20 @@ _WANTED = {
 }
 
 
+def _load_active_generations():
+    """The real registry `_TrackedCancel` records runs in.
+
+    Loaded straight off disk rather than imported, so the extracted class runs
+    against the genuine module without pulling in the whole route package (and
+    without putting studio/backend on sys.path for the rest of the session).
+    """
+    path = SOURCE_PATH.parents[1] / "state" / "active_generations.py"
+    spec = importlib.util.spec_from_file_location("studio_active_generations", path)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
 def _load_registry_module():
     chunks = []
     for n in _TREE.body:
@@ -274,7 +289,7 @@ def _load_registry_module():
             and n.target.id in _WANTED
         ):
             chunks.append(seg)
-    mod = {}
+    mod = {"active_generations": _load_active_generations()}
     exec("import threading, time\n" + "\n\n".join(chunks), mod)
     return mod
 
@@ -674,16 +689,18 @@ def test_generate_stream_cancels_backend_on_stream_cancelled_error():
             body_src = "\n".join(ast.unparse(stmt) for stmt in sub.body)
             found_cancel_handler = (
                 "cancel_event.set()" in body_src
-                and "backend.reset_generation_state()" in body_src
+                and "backend.reset_generation_state(cancel_event)" in body_src
                 and any(isinstance(stmt, ast.Raise) and stmt.exc is None for stmt in sub.body)
             )
         if isinstance(sub, ast.Try) and sub.finalbody:
             final_src = "\n".join(ast.unparse(stmt) for stmt in sub.finalbody)
-            found_finally_cleanup = (
+            # Accumulate: an existence claim, and the cleanup sits in a nested try whose
+            # own finally only unregisters the swap-gate entry.
+            found_finally_cleanup = found_finally_cleanup or (
                 "not completed" in final_src
                 and "not cancel_event.is_set()" in final_src
                 and "cancel_event.set()" in final_src
-                and "backend.reset_generation_state()" in final_src
+                and "backend.reset_generation_state(cancel_event)" in final_src
                 and _awaits_to_thread_gen_close(sub)
             )
 
@@ -731,11 +748,11 @@ def test_stream_chunks_cancel_branch_resets_backend_state():
         ):
             continue
         body_src = "\n".join(ast.unparse(s) for s in sub.body)
-        if "backend.reset_generation_state()" in body_src:
+        if "backend.reset_generation_state(cancel_event)" in body_src:
             return
     raise AssertionError(
         "stream_chunks `if cancel_event.is_set():` branch must call "
-        "backend.reset_generation_state() -- matches the existing "
+        "backend.reset_generation_state(cancel_event) -- matches the existing "
         "request.is_disconnected() / CancelledError cleanup paths and "
         "prevents KV-cache drift after cancel-via-POST"
     )