feat(extensions): complete extension lifecycle and end-to-end workflows #934

PR #577 was the end-to-end completion track for Agent Code's extension platform. It merged on 2026-09-13 as 4855c885. This issue stays open for the deferred items below.

Shipped

• Runtime and views: one API v2 runtime per extension with explicit startup, command and view activation, plus independently mounted sandboxed views. Commands run with no view open, and multiple windows share one runtime. API v1 remains a compatibility path.
• Installs: each install or update is published as an immutable generation that binds bundle bytes, manifest and grants together. Crash, concurrency, update and removal all recover cleanly, and saved data survives uninstall. A same-id bundle from a different source is refused.
• Workspace and input: extension panes work in Dispatch, detach/restore and close/undo without provider processes. Native input is routed by host-minted instance id. Keybindings must be Cmd chords, and first-party chords are reserved.
• Themes: declarative extension themes appear in the picker without running extension code.
• Host services:
  • sessions.observe and storage.
  • Scoped fs.read and fs.write: bounded UTF-8, atomic compare-and-swap, serialized with editor saves.
  • notifications.show: short, extension-attributed toasts.
• Pre-merge review: five Claude reviewers found one blocker and about fifteen should-fix defects. All are fixed in ec17764a except bug(extensions): one unsupported ledger row disables every installed extension #959.

Companions (merged)

• SDK refactor: reshape tree, break up god-files, go all-absolute imports #1, merged as 503bced and released as v0.8.0 on GitHub (not npm).
• Mini Games Track primary and active worktree context #9: four command-routed API v2 modal views.
• Timer Fix post-refactor permission and feed rendering regressions #2: an API v2 background runtime; the countdown and reminders keep running with the panel closed.

Verification

• npm run typecheck passes.
• 735 affected unit, renderer and system tests pass across 104 files.
• Root CI passed on ec17764a, including the quality gate that runs both Electron journeys.
• Earlier in the PR, the real Electron journeys installed the committed Timer and Mini Games bundles.

Deferred

• bug(extensions): one unsupported ledger row disables every installed extension #959: one invalid ledger row disables every installed extension after a rollback past a future API version.
• Not yet verified: full application restart, layout acceptance, and a packaged build.
• Not yet built: transcript and Git reads, prompt and Git mutations, and network access. Each needs explicit authority and integration tests.
• Runtime management UI: background-runtime management beyond the existing Settings failure/retry state.

Plan: docs/superpowers/plans/2026-09-12-extension-platform-completion.md