docs: add FDC3 v3 web guidance for route-scoped identity, context-only apps, and private context types

[Copilot]

Addresses three documentation gaps surfaced by implementer feedback (TraderX + Sail v3) when hosting multiple FDC3 apps on a single origin.

Changes

Route-scoped web app identity (supported-platforms.md, GetAgent.md)

• New "Multiple FDC3 Apps on a Single Origin" section: register each path-differentiated route as a separate AppD record; pass a stable identityUrl matching that record's details.url when calling getAgent() (e.g. for SPAs that have already navigated before getAgent() is called)
• Tips/cautions on URL stability and one-time tokens

Application interop metadata (app-directory/overview.md)

• Replaced a verbose "Context-only Apps" section with a focused paragraph describing the purpose of the interop field in AppD records — intent resolution, catalog discovery, and channel interaction documentation — with links to both the rendered App Directory specification and the raw OpenAPI schema

Private/proprietary context types (context/spec.md)

• New "Private and Proprietary Context Types" section: naming conventions (reverse-domain or org abbreviation), id-vs-custom-fields guidance, privacy considerations for User Channel broadcasts, alternatives for richer point-to-point data sharing, and AppD declaration notes

Related Issue

Resolves #1943

Contributor License Agreement

• I acknowledge that a contributor license agreement is required and that I have one in place or will seek to put one in place ASAP.

Review Checklist

• Issue: If a change was made to the FDC3 Standard, was an issue linked above?
• CHANGELOG: Is a CHANGELOG.md entry included?
• API changes: Does this PR include changes to any of the FDC3 APIs (DesktopAgent, Channel, PrivateChannel, Listener, Bridging)?
  • Docs & Sources: If yes, were both documentation (/docs) and sources updated?
    
    JSDoc comments on interfaces and types should be matched to the main documentation in /docs
  • Conformance tests: If yes, are conformance test definitions (/toolbox/fdc3-conformance) still correct and complete?
    
    Conformance test definitions should cover all required aspects of an FDC3 Desktop Agent implementation, which are usually marked with a MUST keyword, and optional features (SHOULD or MAY) where the format of those features is defined
  • Schemas: If yes, were changes applied to the Bridging and FDC3 for Web protocol schemas?
    
    The Web Connection protocol and Desktop Agent Communication Protocol schemas must be able to support all necessary aspects of the Desktop Agent API, while Bridging must support those aspects necessary for Desktop Agents to communicate with each other
    • If yes, was code generation (npm run build) run and the results checked in?
      
      Generated code will be found at /src/api/BrowserTypes.ts and/or /src/bridging/BridgingTypes.ts
• Context types: Were new Context type schemas created or modified in this PR?
  • Were the field type conventions adhered to?
  • Was the BaseContext schema applied via allOf (as it is in existing types)?
  • Was a title and description provided for all properties defined in the schema?
  • Was at least one example provided?
  • Was code generation (npm run build) run and the results checked in?
    
    Generated code will be found at /src/context/ContextTypes.ts
• Intents: Were new Intents created in this PR?
  • Were the intent name prefixes and other naming conventions & characteristics adhered to?
  • Was the new intent added to the list in the Intents Overview?

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[robmoffat]

Instead of this whole section on context only apps, instead please provide a single paragraph description of the purpose of the interop section of the AppD record, along with a link to the specification of this.

[robmoffat]

@copilot please address the above comment

[Copilot]

Done — replaced the entire "Context-only Apps" section with a single ### Application \interop` Metadata` paragraph that describes the field's purpose and links to the App Directory specification. Commit: the latest push.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.32%. Comparing base (97a4c85) to head (48923c5).

Additional details and impacted files

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##             main    #1969   +/-   ##
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  Coverage   95.32%   95.32%           
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  Files          85       85           
  Lines        6690     6690           
  Branches      932      895   -37     
=======================================
  Hits         6377     6377           
  Misses        313      313           

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[kriswest]

Needs one paragraph restoring, then this should be good to merge

[kriswest]

This should not be removed when making the addition...

[kriswest]

LGTM - can another @finos/fdc3-maintainers team member review and merge, as I have last push on this after committing a suggestion.

[kriswest]

Not sure why test check is stuck...