feat(hosts): add canonical component sets for Zed, Antigravity, and Vibe

[ScriptedAlchemy]

Gap

The compatibility installers expose tracedecay install --agent and Doctor support for three hosts that are absent from the receipt-backed host catalog and therefore have no canonical installer component set:

• Zed — user/global context_servers.tracedecay in settings.json; project-local install is advertised.
• Antigravity — IDE ~/.gemini/antigravity/mcp_config.json plus CLI ~/.gemini/antigravity-cli/plugins/tracedecay.json.
• Mistral Vibe — stdio [[mcp_servers]] in config.toml, prompt rules, managed-skill index, and project-local install.

Required outcome

• Extend the canonical host identity/capability authority for these hosts.
• Define truthful default component sets and receipt-owned artifact/registration paths.
• Route install/update/repair/uninstall through the atomic host-bundle lifecycle.
• Preserve each host's documented ownership constraint (these registrations are direct config edits only where no non-interactive host CLI can express TraceDecay's stdio registration).
• Add rollback/recovery, peer-preservation, Doctor, and sandboxed lifecycle acceptance coverage.

This issue records the gap only; it is intentionally outside PR #707's current host-refresh repair lane.

[ScriptedAlchemy]

Triage against the current PR #707 host lifecycle: this does not generalize as a small component-set catalog extension, so I am leaving it open rather than publishing partial receipt-backed support.

Concrete missing authority by host:

• Zed: the compatibility adapter detects/Doctors settings.json and exposes the primary user path, but has no canonical HostKindV1, no receipt-backed default component set, no component registration readback, and no atomic activate/deactivate projection for either user context_servers.tracedecay or the advertised project-local settings. The implementation needs JSONC-preserving peer-safe edits plus exact backup/rollback for both scopes.
• Antigravity: the adapter Doctors both the IDE and CLI documents, but its current primary registration inventory names only the IDE file. Canonical support must own both ~/.gemini/antigravity/mcp_config.json and ~/.gemini/antigravity-cli/plugins/tracedecay.json in one transaction, preserve unrelated mcpServers, and restore both on failure/recovery.
• Mistral Vibe: the adapter intentionally has no single primary config projection. Support spans peer-preserving TOML [[mcp_servers]], prompt rules, managed-skill export/index state, and the project-local .vibe equivalents. Those need explicit component ownership and rollback boundaries; treating only the MCP config as ContextMcp would make the advertised install receipt incomplete.

The shared blockers are also broader than three match arms: HostKindV1 currently excludes all three, RECEIPT_BACKED_HOST_KINDS excludes them, capability admission/default-component matches are exhaustive, and adding the wire enum requires updating schema/generated consumers and lifecycle acceptance coverage. Each adapter then needs host-specific registration mutation/readback and sandbox tests for install/update/repair/uninstall, foreign-peer preservation, rollback, recovery, and Doctor.

Recommended decomposition: admit the three host identities/capability records together, then land one complete host lifecycle at a time (Zed, Antigravity, Vibe) so no host is reported supported before all of its advertised scopes are receipt-owned and recoverable.

[ScriptedAlchemy]

Integration-lane status (Fable, PR #707 head 04d7f733c): implementation in flight on branch fable/707-closure-793, following the decomposition in the triage comment above and mirroring the Devin footprint from PR #794 (f399b6243) file-for-file. Please do not land a parallel implementation — integrate through this lane (compare patch-ids before pushing).

Slice order: (1) admit HostKindV1::{Zed, Antigravity, Vibe} + descriptors + capability admission + regenerated contracts, with the typed component-set-unavailable refusal until each adapter lands; (2) Zed context_servers.tracedecay in user and project settings.json (JSONC dialect, byte-exact original backup/restore, foreign context_servers.* preserved); (3) Antigravity IDE mcp_config.json + CLI plugins/tracedecay.json as one two-document transaction with rollback of the first write when the second fails and partial state reported as typed degraded, not installed; (4) Vibe [[mcp_servers]] (ContextMcp) and prompt rules (Core) as independently receipted components, VIBE_HOME honoured; (5) docs. Each host ships with install/update/repair/uninstall lifecycle acceptance, rollback, peer preservation, and Doctor readback tests on isolated temp homes.