Skip variants trait-restore when session was explicitly stopped#116
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obj-p merged 1 commit intocli-mcp-parityfrom Apr 16, 2026
Merged
Skip variants trait-restore when session was explicitly stopped#116obj-p merged 1 commit intocli-mcp-parityfrom
obj-p merged 1 commit intocli-mcp-parityfrom
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Follow-up audit from PR #113's deferred items. Walked every MCP handler looking for concurrent-modification races. Summary: No new bugs found — PreviewSession is an actor so within-session state transitions are serialized, and the `preview_snapshot` hole for missing sessions is already fixed in #112. One defensive improvement worth landing: when a concurrent `preview_stop` fires mid-variants-loop, the trait-restore-at-end block would fire against a now-stopped session, producing a misleading "Warning: failed to restore original traits" message for a user who explicitly asked for the stop. Skip the restore when the session is no longer in the registry (iosState for iOS, App.host.allSessions for macOS). No user-visible change for the happy path; the spurious warning goes away for the concurrent-stop case. Documented the remaining concurrent-modification caveat on `handlePreviewVariants`: a second client mutating the same session via preview_configure / preview_switch while variants is mid-loop will interleave its trait change into our capture stream. The daemon intentionally does not hold a per-session lock across tool calls (that's a more invasive architectural change); callers that want deterministic variants should own the session for the duration. All 14 variants integration tests pass unchanged. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Wave 1-C from the deferred-items list on #113: race-condition audit across every MCP handler.
Audit findings
No new bugs found.
PreviewSessionis an actor so within-session state transitions are serialized, and thepreview_snapshothole for missing sessions is already fixed in #112.One defensive improvement landed
When a concurrent
preview_stopfires mid-variants-loop, the trait-restore-at-end block would fire against a now-stopped session, producing a misleading "Warning: failed to restore original traits" message for a user who explicitly asked for the stop. Skip the restore when the session is no longer in the registry (iosStatefor iOS,App.host.allSessionsfor macOS). No user-visible change for the happy path; the spurious warning goes away for the concurrent-stop case.Documented caveat
Added a doc comment on
handlePreviewVariantsspelling out the remaining concurrent-modification limitation: a second client mutating the same session viapreview_configure/preview_switchwhile variants is mid-loop will interleave its trait change into our capture stream. The daemon intentionally does not hold a per-session lock across tool calls (more invasive architectural change); callers that want deterministic variants should own the session for the duration.Test plan
swift buildswift test --filter VariantsCommandTests— 14 integration tests pass unchanged (~60s)🤖 Generated with Claude Code