SMITH-024 Build extension compatibility registry and unsupported-surface UX

[webfish0]

Outcome

Users know whether and how an extension works before relying on it.

Scope

• Static manifest/contribution inspection.
• Activation observation and evidence capture.
• Native/adapted/degraded/external/unsupported classification.
• Explicit handling for webviews, custom editors, notebooks, browser-only APIs, and graphical contributions.
• Extensions view compatibility filters and explanations.

Acceptance criteria

• T-015 passes.
• The release compatibility manifest distinguishes unsupported from untested.

Requirements: FR-013, US-006

Source: backlog.md SMITH-024.

[webfish0]

MVP-4 language and extension compatibility slice landed and was verified on clean commit b1e07b5.

Evidence summary:

• Command: npm run verify:mvp
• Result: passed
• T-014: passed — native extension contributions classify to terminal-safe surfaces
• T-014-language: passed — completion, diagnostics, hover, and code action view models expose terminal-safe data
• T-015: passed — webview/custom editor/notebook graphical surfaces are explicitly unsupported
• T-016-subset: passed — extension configuration, keybindings, and walkthrough textual fallback remain visible to configuration surfaces
• Evidence path from local/CI run: test-evidence/mvp-4-language-extensions/

Known limitation: this slice validates manifest classification and terminal-safe language-feature view models. Live Code OSS extension-host activation and real extension execution remain pending before closing full extension compatibility tasks.