requestExpandedMode(event, "game") does not switch inline webview to the game entrypoint in Playtest

The issue is in the Devvit Web API's requestExpandedMode function. Start by examining the @devvit/web/client module and the EFFECT_WEB_VIEW effect handling. Look for the bridge configuration and entrypoint resolution logic. Check the Playtest environment's webview mode transitions. Verify the immersiveMode flag and entrypoint URL generation. Testing requires a Devvit app setup with multiple HTML entrypoints.

1. Summary

I am seeing unexpected behavior when switching from an inline launch screen to a second expanded entrypoint using the documented Devvit Web API:

default -> splash.html -> trusted click -> requestExpandedMode(event, "game") -> game.html

The splash screen loads correctly, but the webview remains inline after the click and game.html never opens.

2. Environment

• App: ai-content-helper
• Devvit app/runtime version: 0.0.14.95
• SDK: 0.14.4
• Playtest subreddit: r/ai_content_helper_tes
• Client: Reddit Web
• Playtest environment: Devvit Playtest
• Registered entrypoints:

{
  "post": {
    "entrypoints": {
      "default": {
        "entry": "splash.html"
      },
      "game": {
        "entry": "game.html"
      }
    }
  }
}

3. Expected behavior

The post should initially render splash.html in inline mode.

After the user clicks the Start button, the app should:

1. enter expanded mode;
2. load the game entrypoint;
3. display game.html.

4. Actual behavior

• splash.html loads successfully.
• devvit.webViewMode before the click is 1 (inline).
• The Start button receives a real trusted user click.
• The handler calls requestExpandedMode(event, "game").
• After the click:
  • devvit.webViewMode remains 1 (inline);
  • the iframe remains on splash.html;
  • no game.html frame is opened;
  • no visible transition occurs.

5. Minimal reproduction

Minimal configuration:

{
  "post": {
    "entrypoints": {
      "default": {
        "entry": "splash.html"
      },
      "game": {
        "entry": "game.html"
      }
    }
  }
}

Minimal client flow:

splash.html
  -> Start button
  -> trusted click event
  -> requestExpandedMode(event, "game")
  -> expected: expanded game.html

The splash handler is equivalent to:

import {requestExpandedMode} from "@devvit/web/client";

startButton.addEventListener("click", event => {
  requestExpandedMode(event, "game");
});

6. What was already verified

• The splash entrypoint loads normally.
• The click is a trusted user click.
• The app starts in inline mode.
• The game entrypoint exists in the bridge configuration.
• The game key matches the devvit.json entrypoint key.
• The local SDK 0.14.4 implementation generates an EFFECT_WEB_VIEW effect with:
  • immersiveMode: IMMERSIVE_MODE;
  • the resolved game.html entrypoint URL.
• The source builds successfully.
• Typecheck, lint, unit tests, and build pass.
• No temporary diagnostic code remains in the app.

7. What was already ruled out

The following errors were not observed:

• web view is already expanded;
• Untrusted event;
• no entrypoint named "game";
• JavaScript page errors;
• browser console errors related to the transition;
• scheduler, backend, Redis, Gemini, or automation errors.

The issue does not appear to be caused by the automation or backend logic. Those components are unrelated to the splash-to-game transition.

An independent direct submitCustomPost({entry: "game"}) test was not completed because the current Playtest workflow did not expose the temporary diagnostic menu action, and the temporary webview endpoint returned 404. No conclusion is being made from that incomplete test.

8. Relevant logs/errors

Observed after clicking Start:

Before click:
devvit.webViewMode === 1 // inline

After click:
devvit.webViewMode === 1 // still inline
Current frame:
...-webview.devvit.net/splash.html

No JavaScript or page errors were reported.

No errors were reported for:

already expanded
Untrusted event
no entrypoint named "game"

9. Question to Devvit maintainers

Could you confirm whether this behavior is expected in Reddit Web Playtest for Devvit SDK 0.14.4 / app version 0.0.14.95?

Specifically:

1. Is EFFECT_WEB_VIEW with IMMERSIVE_MODE expected to switch from default to game in Reddit Web Playtest?
2. Are there known limitations involving multiple HTML entrypoints or expanded mode in Playtest?
3. Is there an official way to create or open a post directly with entry: "game" for validation?
4. Are additional browser/client requirements or flags needed for this transition?

No claim is being made that this is a Reddit bug. This report is intended to provide a minimal reproduction of unexpected behavior and request guidance.