Add webview communication with the frontend

[TimoPtr]

Proposed change

Add a small mermaid diagram explaining how the communication with the frontend is working in the Android app.

Type of change

• Document existing features within Home Assistant
• Document new or changing features for which there is an existing pull request elsewhere
• Spelling or grammatical corrections, or rewording for improved clarity
• Changes to the backend of this documentation
• Remove stale or deprecated documentation

Checklist

• I have read and followed the documentation guidelines.
• I have verified that my changes render correctly in the documentation.

Additional information

• Link to relevant existing code or pull request: Introduce frontend message handler android#6383

Summary by CodeRabbit

• Documentation
  • Added a WebView communication architecture section to Android docs, including an architecture overview, an interaction diagram illustrating message flow, and a "Component responsibilities" subsection detailing the public-facing components and their roles.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📝 Walkthrough

Walkthrough

A new documentation section titled "WebView communication architecture" is added to the Android architecture guide, detailing the communication flow between Home Assistant Frontend JS and internal Android components, including architecture overview and component responsibilities. This is a documentation-only addition with no code or behavior changes.

Changes

Cohort / File(s)	Summary
Android architecture documentation docs/android/architecture.md	Added new "WebView communication architecture" section with component interaction overview, Mermaid diagram describing data flow between FrontendJsBridge, FrontendMessageHandler, FrontendExternalBusRepository, and ServerSessionManager, and detailed component responsibilities subsection.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: adding documentation about WebView communication with the frontend in the Android app context.
Description check	✅ Passed	The description follows the template with all required sections completed: Proposed change is filled (with diagram image), Type of change is checked, both checklist items are marked complete, and relevant PR link is provided.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch android/webview_architecture

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

docs/android/architecture.md (1)

119-119: Consider clarifying the arrow label for consistency.

The label "FrontendJsHandler" appears to reference an interface or type, while other labels in the diagram use method names or actions (e.g., "getExternalAuth()", "onMessageReceived()"). Consider making this label more descriptive to match the pattern, such as "implements FrontendJsHandler" or "via FrontendJsHandler".

📝 Suggested clarification

-    JsBridge -->|"FrontendJsHandler"| MsgHandler
+    JsBridge -->|"via FrontendJsHandler"| MsgHandler

or

-    JsBridge -->|"FrontendJsHandler"| MsgHandler
+    JsBridge -->|"implements FrontendJsHandler"| MsgHandler

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@docs/android/architecture.md` at line 119, The diagram arrow label
"FrontendJsHandler" is ambiguous compared to other action/method labels; update
the label between JsBridge and MsgHandler to a descriptive phrase like
"implements FrontendJsHandler" or "via FrontendJsHandler" so it matches the
pattern of method/action labels (reference: JsBridge, FrontendJsHandler,
MsgHandler).

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@docs/android/architecture.md`:
- Line 92: The two broken links in the sentence referencing external
authentication and external bus need updating: replace the paths
`/docs/api/native-app-integration/frontend/external-authentication` and
`/docs/api/native-app-integration/frontend/external-bus` with the correct
`/docs/frontend/external-authentication` and `/docs/frontend/external-bus`
respectively so the WebView paragraph links point to the actual documentation
pages.

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Nitpick comments:
In `@docs/android/architecture.md`:
- Line 119: The diagram arrow label "FrontendJsHandler" is ambiguous compared to
other action/method labels; update the label between JsBridge and MsgHandler to
a descriptive phrase like "implements FrontendJsHandler" or "via
FrontendJsHandler" so it matches the pattern of method/action labels (reference:
JsBridge, FrontendJsHandler, MsgHandler).

[TimoPtr]

@jpelgrom do we wait for it to be use before merging this?

[jpelgrom]

Mermaid styling seems to need some tweaks for dark mode...

do we wait for it to be use before merging this?

Yes I'd wait until this is actually how the main WebView works, we might tweak it while developing.

[silamon]

From what I understand, this isn't ready for merge yet, hence setting as draft.

[TimoPtr]

From what I understand, this isn't ready for merge yet, hence setting as draft.

Exactly. I'll handle the merge, once the migration is going to be over. We are merging small bits at the time in debug only in the app. I'm going to probably keep this PR for a while and might update it along the way. The progress can be tracked in home-assistant/android#6424