Files Changed: adopt app and extension user mutation routes

Acceptance Criteria

• User-initiated file operations bind to the initiating panel and active session before storage work begins.
• Sidebar create, move, Trash, restore, directory, and recursive operations use registered contexts or deny before mutation in full-provenance mode.
• Preview and Files Changed editing cannot bypass host-mediated context validation.
• A capability-discovery legacy result preserves existing behavior with a visible legacy label; an invalid mutation context never falls back to untracked mutation.
• Watchers only revalidate server-owned receipts and cannot determine ownership or lifecycle locally.
• User-originated receipts remain distinguishable from agent, child-agent, and system receipts.

Testing Decisions

• Extend extension-host, panel ownership, Sidebar, Preview, review-editing, watcher, and legacy-fallback tests.
• Add paired app-extension integration coverage for invalid context denial and exact idempotent retry.

Key Decisions

• Browser code never receives a mutation capability or determines externality.
• User actions are first-class session origins, not anonymous filesystem events.

Constraints & Invariants

• Existing Files Changed: session-bind Sidebar external file mutations #976 remains a foundation and is not rewritten around a merged v1 implementation.
• UI transport never exposes host-only paths, hashes, evidence, or capabilities.

Prior Art

• Parent Files Changed: full session-lineage mutation ledger #972
• Existing Files Changed: session-bind Sidebar external file mutations #976 and its merged extension implementation

Deliberation Resolution

• The browser sends a display-safe MutationIntent containing operation, user-selected display target, and idempotency key. The extension host resolves resource identity, snapshots the active panel and session before input or confirmation, obtains the context, and returns only a display-safe operation result.
• Capability discovery has full, partial, legacy, and unavailable outcomes. Only legacy selects existing behavior; partial uses a labelled partial epoch, while invalid or expired mutation contexts deny without fallback.
• All user operations consume the operation-group contract from Files Changed: enforce mutation registry, contexts, and resource identity #1077: the same idempotency key returns the prior result, preflight failures have no applied resources, and execution failures return explicit partial outcomes.
• Watchers receive only receipt references and assessment revisions, emit invalidation, and never receive or derive ownership, lifecycle, canonical paths, hashes, or evidence.
• Test fixtures from Files Changed: session-bind Sidebar external file mutations #976 provide legacy reservation behavior; Files Changed: enforce mutation registry, contexts, and resource identity #1077 and Files Changed: enforce provenance privacy and serializer policy #1078 provide full-mode context and display-safe transport fixtures.

Source

Part of #972. Blocked by #976, #1077, and #1078.