Migrate snapshot to daemon client with magical reuse#102
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obj-p merged 2 commits intocli-mcp-parityfrom Apr 15, 2026
Merged
Migrate snapshot to daemon client with magical reuse#102obj-p merged 2 commits intocli-mcp-parityfrom
obj-p merged 2 commits intocli-mcp-parityfrom
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Third PR in the CLI/MCP parity stack. `snapshot` becomes a thin daemon client that reuses an existing preview session when one is running for the target file, and falls back to an ephemeral session otherwise (create → capture → stop). No more in-process NSApplication + preview compile from `snapshot` itself — all of that moves into the daemon. The magical resolution: - `--session <uuid>` wins if passed. - `--file <path>` (or the positional file arg): if exactly one active session has that source file, reuse it; else error on ambiguity, or ephemeral on miss. - No flag: if exactly one session is running, reuse it. Changes: - New SessionResolver: uses the new `session_list` MCP tool to map CLI flags to a session ID. Clear error messages on ambiguity or missing session. - New `session_list` MCP tool: returns one tab-delimited line per active session (iOS + macOS). Used by SessionResolver; also useful for future discovery commands. - SnapshotCommand rewrite: AsyncParsableCommand using DaemonClient. Handles both reuse and ephemeral paths. Traits are applied only on ephemeral start; reusing a session that was configured differently prints a note and snapshots with the session's current traits. Format is inferred from the output file extension (`.png` → PNG, `.jpg`/`.jpeg` → JPEG) unless `--quality` is explicit. - Platform resolution moved client-side. Previously the daemon called `inferredPlatformAsync` when no `--platform` was passed, which could hang on xcodeproj sources: the walk-up for Package.swift falls through to the repo root, then `swift package describe` runs on a large package and can sit forever. New `findPackageDirectory` short-circuits when it crosses an xcodeproj/xcworkspace/WORKSPACE boundary before finding Package.swift, returning nil instead. SnapshotCommand resolves platform locally and always passes an explicit `platform` to the daemon. - Fix MCP tool arg names: `project` → `projectPath`, `device` → `deviceUDID`. RunCommand had the same bug; fixed there too. - PreviewsMacOS.PreviewHost exposes `allSessions` so the new `session_list` tool can enumerate macOS sessions alongside iOS. - DaemonTestLock wraps every SnapshotCommandTests case, matching the pattern used by RunCommandTests and DaemonLifecycleTests — without it, the daemon state races across suites when they run in parallel. - SnapshotCommand and RunCommand no longer live in the "needs NSApplication" branch of PreviewsMCPApp.main. They're pure daemon clients. Test plan: - 13 existing snapshot tests still pass (with daemon path instead of in-process). - 243/243 non-iOS tests pass in the full concurrent sweep. - Manual: `previewsmcp run --detach` then `previewsmcp snapshot <same file>` captures the live window in ~0.4s vs ~30s for a cold ephemeral. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Five small improvements from the review: 1. Surface preview_stop failures on ephemeral teardown. Extract stopEphemeralSession helper so a failed stop logs a warning instead of being silently swallowed by `try?`. Leaked sessions in a long-lived daemon could otherwise confuse future reuse matching. 2. Remove the dead `if lines.isEmpty` branch in handleSessionList — `[].joined(separator:)` already produces "". 3. Extract SessionResolver.resolveAgainst as a pure (no MCP client) function expressing the resolution policy. Makes the three decision branches (file-matches / file-ambiguous / sole-session) explicit and testable in principle, even though the current test targets are structured such that we exercise them through the integration tests rather than import-based unit tests. 4. Regression tests for findPackageDirectory's non-SPM boundary detection: one for xcodeproj-sibling, one for Bazel WORKSPACE. Guards against reintroducing the hang we chased down in #102. 5. New integration test: "Snapshot reuses an already-running session instead of ephemeral". Starts a detached run, then snapshots the same file, and asserts the snapshot completes in under 2s — reuse is sub-second whereas ephemeral is 5+ seconds. Proves the magical resolution actually reuses sessions rather than silently falling through to ephemeral. 30/30 daemon-touching tests pass in the targeted sweep. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This was referenced Apr 15, 2026
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Summary
Third PR in the CLI/MCP parity stack. `snapshot` becomes a thin daemon client that reuses an existing preview session when one is running for the target file, and falls back to an ephemeral session otherwise.
Observed behavior
Live-session reuse is ~80× faster than cold ephemeral:
Test plan
Related
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