fix(studio): update WebMCP test for polyfill fallback - #3532
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The "registers nothing when the browser has no WebMCP" test asserted that document.modelContext was absent after mount. Since #3514 added the @mcp-b/global polyfill fallback, the hook now installs document.modelContext even when the browser has no native support — that is the polyfill's job. The real assertion is that mounting does not throw, which still holds. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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* feat(studio): let an agent drive Studio's selection and playhead
Adds `studio_select` and `studio_seek`, so an agent and the human are looking
at the same element and the same instant. Selecting reveals the inspector,
exactly as a click does, which is what makes the agent's move visible.
Selection is shared state, not a per-call argument, and that is forced rather
than chosen. Most of Studio's edit handlers read the ambient React selection,
and `applyDomSelection` only schedules a state update, so selecting and
committing inside ONE call would write to whatever was selected before. Two
tool calls are separated by a render, so the contract is select first, then
act. That is also how a human works: click, then type.
`studio_seek` uses `requestSeek`, not `setCurrentTime`. The latter only moves
the timeline's displayed number and leaves the composition where it was.
Two things the tools refuse to fake:
Seek does not clamp. `seek()` already clamps against the adapter's duration,
which can differ from the store's, and clamping again would give that
invariant two owners that can disagree. The tool reports where the playhead
actually landed instead, read back afterwards.
`requestSeek` is fire-and-forget, so it cannot report that no adapter was
mounted to receive it. The tool compares the playhead before and after and
fails rather than claiming a seek that never happened.
Select separates three failures that a single message would have merged: the
preview is not mounted yet (wait), no element matches the handle (re-read),
and the element cannot be selected (try a neighbour). The agent's next move
differs for each, so collapsing them would cost it a round trip or a retry
loop.
* feat(studio): give an agent eyes with studio_frame
Renders the composition to a PNG at a given time and returns the URL. This is
what turns the tool set from a remote control into a loop: author a change,
capture the instant it affects, look, adjust. No agent can judge motion from
source, because "what does this look like at 2.4 seconds" is not a question a
file answers.
Reuses Studio's existing capture endpoint via `buildFrameCaptureUrl` rather
than inventing a second one.
Two things this does not fake:
It reports the time the playhead LANDED on, not the time requested. The player
clamps, so those differ at the ends, and attaching the wrong time to a frame is
how an agent draws a confident wrong conclusion about motion.
It waits before capturing, by default 150ms. The frame is rendered from the
file on disk, and the render cache is cleared by a file watcher with a 40ms
write-stability threshold, so a capture that beats the watcher renders the
PRE-edit composition. That exact staleness was a real bug here once. An agent
reading a stale frame as "my edit failed" would thrash, so the wait is on by
default, `settleMs` makes it tunable, and the tool description names the
failure rather than leaving it to be rediscovered.
It probes with HEAD before returning, so a URL that 404s comes back as a
failure with a hint instead of as a link the agent cannot render.
* feat(studio): add studio_inspect, so an agent reads before it writes
Everything about one element in one call: resolved styles, text fields, box,
data attributes, GSAP animations, and what the element will and will not
accept.
The point is to prevent a failed write rather than to satisfy curiosity.
`can.reasonIfDisabled` is passed through verbatim from Studio's own
capabilities, so an agent that reads first should never attempt an edit the
element would refuse.
Three things it refuses to get wrong:
Animations are reported ONLY for the current selection, because that is the
only element Studio parses them for. Attributing them to any other element
would be reporting the wrong element's motion, which is worse than reporting
none. When a handle names something else the field is empty and
`animationEditingBlocked` says why.
`animationEditingBlocked` also carries the two states where animation editing
is off entirely, multiple timelines and an unsupported timeline pattern. Both
live on the selection context. Learning them from a read costs one call;
learning them from a failed write costs a retry loop.
Inspecting a handle does NOT change what is selected. It is a read, and
stealing the human's selection would be a side effect they did not ask for.
There is a test asserting `applySelection` is never called.
Nothing selected and no handle given is a failure, not an empty result. An
empty result would assert "this element has nothing", which is a different and
false claim.
* feat(studio): let an agent edit text and styles, guarded
The first tools that change the composition. Both act on the current
selection and take no handle, which is forced rather than chosen: the
handlers read the ambient React selection, and `applyDomSelection` only
schedules a state update, so selecting and committing inside one call would
write to whatever was selected before. Select first, then edit.
Also plumbs the write-blocked state, which was the blocker for shipping any
write at all. `domEditSaveQueuePaused` and the external-file conflict both
lived on App and were unreachable from the tool surface, so `canWrite` was
optimistic and a comment said so. They now derive into a single
`writeBlockedReason` on the shell context: one field, one owner, conflict
taking precedence because resolving it is what unblocks the queue.
That guard matters more than it looks. Both states are BANNERS in Studio with
no lock behind them, so nothing else was stopping a programmatic write from
landing on top of a conflict the user had been asked to adjudicate.
Three things the tools refuse to fake:
They check the outcome, not the absence of a throw. Studio has several paths
where a failed commit resolves anyway, so awaiting the handler proves nothing.
The tagged outcome added earlier is what proves the write landed.
A partial style result is reported as partial. `handleDomStyleCommit` is one
property per call, so N properties are N commits; the result carries `applied`
and `rejected` maps rather than a single boolean that would have to pick a
side.
Style commits run sequentially, never concurrently. Two commits racing through
Studio's client-side read-modify-write can record undo entries that both claim
the same starting content. There is a test that measures concurrency rather
than trusting the loop.
Every decline reason maps to a hint naming what to do instead, so a refusal
routes the agent rather than just stopping it.
* feat(studio): move, resize and rotate, verified by reading back
`studio_transform` does what a drag does, and then checks. The box in the
result is READ BACK after the write, never echoed from the request, and
`applied` lists what actually took effect.
That is not belt-and-braces. The plan for this unit said to re-derive the
geometry handlers' behaviour rather than trust any description of them, and
doing that turned up three different behaviours behind one interface.
The handlers on `DomEditActionsValue` are the GSAP-AWARE wrappers, aliased in
`useDomEditSession.ts:534-538`, not the CSS ones in `useDomGeometryCommits.ts`
that an earlier note in this workstream described.
`handleGsapAwarePathOffsetCommit` and `handleGsapAwareRotationCommit` are
`if (gsapCommitMutation) { ...intercept... }` with no else branch. Their own
comments say the absence is deliberate: position and rotation are written as
GSAP code and there is no CSS fallback to write to. So they can return having
done nothing.
`handleGsapAwareBoxSizeCommit` is not like the other two. It runs through
`runGestureTransaction` with separate scale and width/height routes, so resize
works more generally.
Reading back is what turns that middle case from a silent lie into a reported
one. A move that did nothing comes back in `unchanged` with a reason.
Three smaller decisions:
Operations re-read between each other, so a move is judged against the box
AFTER a resize in the same call. Comparing against the original would credit
the resize's change to the move.
Rotation is reported as dispatched, not verified. `rotate` is an individual
transform property and does not appear in the computed transform, so there is
no honest box-derived signal, and claiming one would be worse than saying so.
x pairs with y and width pairs with height. Accepting one alone would mean
inventing the other from the current value, which moves the element somewhere
the caller did not ask for. The pairing rule and its minimum live in one
`parsePair` helper rather than as four separate branches.
* feat(studio): let an agent author motion
Four tools: add an animation, change its duration/ease/position, add a
keyframe, delete it. This is the capability that makes the tool set worth
having, because motion is the one thing an agent cannot judge or author from
source.
These are deliberately less confident than the rest of the set, and the
reason is the handlers underneath them:
`handleGsapAddAnimation(method)` takes only a method. Its insert position
comes from the live playhead, not the caller, and the call is `void ...catch()`
so it returns nothing.
`handleGsapAddKeyframeBatch` returns a promise but catches its own failure, so
awaiting proves the call finished, not that it landed.
`handleGsapDeleteAnimation` discards its promise entirely.
`handleGsapUpdateMeta` is the one honest signal. It returns a boolean.
U8 handled the same problem by reading the result back. That does not work
here: the animation list comes from React state that only refreshes on a
render, and no render happens inside one tool call. Rather than fake a
verification with a frame-timer, these report what was DISPATCHED and the
descriptions tell the agent to call studio_inspect to see the result. Saying
"I asked for this" is honest; saying "this happened" would not be.
Three consequences worth stating:
`studio_add_animation` takes no position. The handler reads the playhead, so
accepting one would report a number that had no effect. It reports where the
playhead actually was and tells the agent to seek first.
`studio_update_animation` rules out the no-selection case BEFORE dispatch. The
handler answers `false` for both "nothing selected" and "the write failed", so
eliminating one is what makes the other legible.
Keyframe percent and properties are validated in the tool, because nothing in
the platform checks input against the declared schema.
* feat(studio): add studio_inspect, so an agent reads before it writes (#3517)
Everything about one element in one call: resolved styles, text fields, box,
data attributes, GSAP animations, and what the element will and will not
accept.
The point is to prevent a failed write rather than to satisfy curiosity.
`can.reasonIfDisabled` is passed through verbatim from Studio's own
capabilities, so an agent that reads first should never attempt an edit the
element would refuse.
Three things it refuses to get wrong:
Animations are reported ONLY for the current selection, because that is the
only element Studio parses them for. Attributing them to any other element
would be reporting the wrong element's motion, which is worse than reporting
none. When a handle names something else the field is empty and
`animationEditingBlocked` says why.
`animationEditingBlocked` also carries the two states where animation editing
is off entirely, multiple timelines and an unsupported timeline pattern. Both
live on the selection context. Learning them from a read costs one call;
learning them from a failed write costs a retry loop.
Inspecting a handle does NOT change what is selected. It is a read, and
stealing the human's selection would be a side effect they did not ask for.
There is a test asserting `applySelection` is never called.
Nothing selected and no handle given is a failure, not an empty result. An
empty result would assert "this element has nothing", which is a different and
false claim.
* feat(studio): move, resize and rotate, verified by reading back (#3519)
`studio_transform` does what a drag does, and then checks. The box in the
result is READ BACK after the write, never echoed from the request, and
`applied` lists what actually took effect.
That is not belt-and-braces. The plan for this unit said to re-derive the
geometry handlers' behaviour rather than trust any description of them, and
doing that turned up three different behaviours behind one interface.
The handlers on `DomEditActionsValue` are the GSAP-AWARE wrappers, aliased in
`useDomEditSession.ts:534-538`, not the CSS ones in `useDomGeometryCommits.ts`
that an earlier note in this workstream described.
`handleGsapAwarePathOffsetCommit` and `handleGsapAwareRotationCommit` are
`if (gsapCommitMutation) { ...intercept... }` with no else branch. Their own
comments say the absence is deliberate: position and rotation are written as
GSAP code and there is no CSS fallback to write to. So they can return having
done nothing.
`handleGsapAwareBoxSizeCommit` is not like the other two. It runs through
`runGestureTransaction` with separate scale and width/height routes, so resize
works more generally.
Reading back is what turns that middle case from a silent lie into a reported
one. A move that did nothing comes back in `unchanged` with a reason.
Three smaller decisions:
Operations re-read between each other, so a move is judged against the box
AFTER a resize in the same call. Comparing against the original would credit
the resize's change to the move.
Rotation is reported as dispatched, not verified. `rotate` is an individual
transform property and does not appear in the computed transform, so there is
no honest box-derived signal, and claiming one would be worse than saying so.
x pairs with y and width pairs with height. Accepting one alone would mean
inventing the other from the current value, which moves the element somewhere
the caller did not ask for. The pairing rule and its minimum live in one
`parsePair` helper rather than as four separate branches.
* docs: document Studio's WebMCP agent tools, proven end-to-end in a browser (#3521)
* docs: document Studio's WebMCP agent tools
Adds `guides/webmcp`, under Developers > Agent setup.
Its first job is to defuse a name collision. `guides/mcp` already exists and
covers HeyGen's HOSTED MCP connector, which builds a video from a chat. This
page is about an agent working inside Studio on a composition already open in
front of you. Different feature, confusingly similar name, so the page says
what it is not before it says what it is.
Written to DOCS_GUIDELINES: one-sentence intro, outcome before implementation,
real values rather than placeholders, and three callouts.
The three things a reader most needs are the ones easiest to get wrong:
The API is `document.modelContext`, not `navigator.modelContext`. Most
published examples use the second, which is a polyfill compatibility shim
rather than a spec member, so feature-detecting it misleads.
Select first, then edit. Most editing tools act on the current selection, and
an agent that skips it gets an error rather than a wrong-element write.
Leave Studio visible. Some of Studio's write paths report failure through a
toast rather than a return value, so the human is the one who sees it. That is
a real property of the co-pilot design, not a nicety, so the page says it
plainly.
Verified with `npx mint validate` and `npx mint broken-links --check-redirects`,
both passing.
* fix(studio): target the text field that exists, not one named self
Found by running the tools end to end in a browser, which is the only way it
could have been found: the unit tests mock `setText`, so they never crossed the
boundary where this breaks.
An element's text usually lives in a CHILD field, keyed like `self:0:h1` or
`child:0:h1`. `studio_set_text` passed no field key, so
`buildNextDomTextFields` planned zero operations, the request went out with an
empty patch, and the server answered:
POST /api/projects/<id>/file-mutations/patch-element
-> 400 {"error":"target and operations required"}
Which surfaced as `persist-failed`. The tool was telling the truth, so the
reporting work in the earlier PRs did its job, but the failure looked like a
server problem and was not.
The tool now resolves the field: the one the caller named, or the element's
single field when it has exactly one. An element with several fields is asked
to name one; an element with none is reported blocked. Naming a field the
element does not have is rejected with the list of the ones it does have,
rather than silently writing nowhere.
Four regression tests, including the exact `child:0:h1` shape that failed. One
existing assertion changed: it expected the field to be `undefined`, which is
precisely the bug, so it now expects the resolved key.
Also documents two things the browser run surfaced, both real and neither a
defect: registration is asynchronous, so a caller reading `getTools()` too
early sees a partial list; and the tools that act on the current selection need
a render between the select and the edit, which a real agent gets for free
because its calls arrive as separate messages.
* docs: give the agent-tools kill switch instructions that work
The page told readers to set agentToolsEnabled in Studio's preferences.
Nothing writes that flag: it is read in useStudioAgentTools and parsed in
studioUiPreferences, but there is no settings UI and no toggle, so the
instruction could not be followed. Replace it with the localStorage write
that actually flips it, and spell out the merge, since overwriting the key
drops every other stored preference.
* docs: do not promise a per-call permission prompt we have not verified
The page said the browser asks before any agent calls a tool. Prompt
granularity is browser-specific and unsettled during the origin trial, and
we have not observed it on the native path. Say what holds, that access is
gated, and name the part that is still moving.
* fix(studio): re-apply WebMCP test polyfill fix (#3532 regression)
The squash merge of #3518 re-introduced the old assertion that
document.modelContext is absent. The polyfill from #3514 installs it
as a fallback — that is expected behavior.
Same fix as #3532: remove the assertion, keep the boot-cleanly contract.
---------
Co-authored-by: miga-heygen <miguel.sierra_miga@heygen.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
useStudioAgentToolstest "registers nothing when the browser has no WebMCP" asserteddocument.modelContextwas absent after mount@mcp-b/globalpolyfill, the hook installsdocument.modelContexteven without native browser support — that's the polyfill's purposeThis fixes the
CI / Testfailure onmain.Other main CI failures (not ours)
npm error notarget No matching version found for mint@4.2.837(docs tool dependency)ECONNREFUSED ::1:3000(Windows network test infra)Test plan
useStudioAgentToolstests pass withNODE_ENV=development— Miga
🤖 Generated with Claude Code