fix(scenes): hold host commands until the ready handshake

[karngyan]

Fixes the console error reported in karnstack/karnstack#153:

Failed to execute 'postMessage' on 'DOMWindow': The target origin provided
('http://localhost:8788') does not match the recipient window's origin
('http://localhost:8080').

Root cause

The failing direction is parent to host, not host to parent as the issue guessed (the scene host posts with parentOrigin: "*", which never mismatches).

A freshly created iframe holds an about:blank document that inherits the embedding page's origin until the real host document loads. send() targets the host origin resolved from src, so any command posted in that window is refused by the browser and surfaces as a console error.

ScenesPlayer hits this on every cross-origin embed: React runs child effects first, so Player mounts the iframe and then ScenesPlayerInner's sceneTheme effect immediately posts a kino:setTheme into a frame that is still about:blank.

Fix

Gate send() on the kino:ready handshake, the earliest point at which the host is both on its own origin and listening (before then a delivered message would be dropped anyway, since the host has not attached its listener). Nothing is lost: the pre-ready rate, volume, muted and theme all ride the kino:init reply.

The picture-in-picture mirror is about:blank on the pip window's origin under the same rule, so sendMirror() gates on the mirror's own handshake, reset when a mirror is created and when pip closes.

Tests

Two new cases pin the invariant for the master and the mirror, including that pre-ready settings still arrive via kino:init. Three existing tests posted commands without the handshake (encoding the buggy behavior) and now perform it first. Full suite: 212 passing, typecheck and lint clean.

Summary by CodeRabbit

• Bug Fixes
  • Improved scene synchronization during iframe loading by delaying commands until the connection is ready.
  • Ensured playback settings such as volume, rate, mute state, and theme are applied reliably during initialization.
  • Improved Picture-in-Picture synchronization when starting or ending a session.
• Tests
  • Added coverage verifying that commands are withheld before readiness and delivered correctly afterward.

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Workers

The latest updates on your project. Learn more about integrating Git with Workers.

Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	kino	6206cc1	Commit Preview URL Branch Preview URL	Jul 24 2026, 09:53 PM

[coderabbitai]

📝 Walkthrough

Walkthrough

Scenes messaging now waits for kino:ready from the host and picture-in-picture mirror before sending commands. Readiness resets across PiP lifecycle and provider destruction, with tests covering deferred initialization and post-ready command delivery.

Changes

Scenes readiness gating

Layer / File(s)	Summary
Host readiness gate src/scenes/provider.ts, src/scenes/provider.test.ts, .changeset/scenes-post-before-host-ready.md	Host commands are suppressed until kino:ready; subsequent initialization carries the current scene state, and destruction disables further host messaging.
Picture-in-picture readiness lifecycle src/scenes/provider.ts, src/scenes/provider.test.ts	Mirror commands wait for the mirror handshake, readiness resets for new or closed PiP sessions, and tests cover deferred initialization and post-ready fan-out.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant ScenesProvider
  participant HostIframe
  participant PipMirror
  HostIframe->>ScenesProvider: kino:ready
  ScenesProvider->>HostIframe: kino:init with current settings
  PipMirror->>ScenesProvider: kino:ready
  ScenesProvider->>PipMirror: kino:init with current mirror state
  ScenesProvider->>HostIframe: Send transport or scene command
  ScenesProvider->>PipMirror: Send mirrored command

Loading

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely captures the main change: scenes now wait for the ready handshake before sending host commands.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/scenes-post-before-host-ready

---

_{Comment @coderabbitai help to get the list of available commands.}

[karngyan]

@coderabbitai review

[coderabbitai]

✅ Action performed

Review finished.

Note: CodeRabbit is an incremental review system and does not re-review already reviewed commits. This command is applicable only when automatic reviews are paused.

[coderabbitai]

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

src/scenes/provider.ts (1)

173-183: 🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Send kino:init before notifying subscribers.

Line 175 synchronously emits to subscribers while ready is already true. A subscriber that invokes an action can post a control command before kino:init; the later init may then override that command (for example, autoPlay). Send the init reply before patch({ duration }).

Proposed fix

 case "kino:ready":
   ready = true
-  patch({ duration: msg.duration })
   send({
     type: "kino:init",
     rate: desiredRate,
     volume: state.volume,
     muted: state.muted,
     autoPlay: opts.autoPlay ?? false,
     theme,
   })
+  patch({ duration: msg.duration })
   break

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/scenes/provider.ts` around lines 173 - 183, In the initialization flow,
move the kino:init send() call before patch({ duration }) so subscribers are
notified only after the initialization reply has been emitted. Preserve ready =
true before send(), and keep the existing init payload unchanged.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@src/scenes/provider.ts`:
- Around line 173-183: In the initialization flow, move the kino:init send()
call before patch({ duration }) so subscribers are notified only after the
initialization reply has been emitted. Preserve ready = true before send(), and
keep the existing init payload unchanged.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 1a346907-630b-4407-b712-924d114f97e0

📥 Commits

Reviewing files that changed from the base of the PR and between 0a1ba5c and 6206cc1.

📒 Files selected for processing (3)

• .changeset/scenes-post-before-host-ready.md
• src/scenes/provider.test.ts
• src/scenes/provider.ts