Add configure command for live trait changes#103
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obj-p merged 2 commits intocli-mcp-parityfrom Apr 15, 2026
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Fourth PR in the CLI/MCP parity stack. \`previewsmcp configure\` forwards trait changes to the daemon's \`preview_configure\` MCP tool. Session targeting mirrors \`snapshot\`: - \`--session <uuid>\` — explicit - \`--file <path>\` — resolve by source file - no flag — use the sole running session Unlike \`snapshot\`, there's no ephemeral fallback: configuring a session that doesn't exist is an error (suggesting \`run --detach\` as the remedy). Supported traits: - \`--color-scheme\` (light / dark) - \`--dynamic-type-size\` (xSmall..accessibility5) - \`--locale\` (BCP 47) - \`--layout-direction\` (leftToRight / rightToLeft) - \`--legibility-weight\` (regular / bold) Pass an empty string to clear a trait (matches the daemon's signal for reverting an earlier override). Validation happens client-side via \`PreviewTraits.validated\` so bad values fail before an RPC round-trip. Empty strings are allowed through as the clear-signal. Tests (5): validation rejects missing traits, validation rejects invalid values, no-session error path, dark-mode round-trip (snapshot before + after verifies the change actually took effect), and --session explicit targeting. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
The review of PR #103 caught a real bug: every layer advertised that passing an empty string to preview_configure would clear a trait override, but the implementation silently preserved the existing value. Root cause: parseTraits normalized empty strings to nil, then PreviewSession.reconfigure used PreviewTraits.merged which does `other.field ?? self.field` — nil in `other` keeps self's value. There was no way to signal "clear this field" through the pipeline. Fixes: - Add PreviewTraits.Field enum + PreviewTraits.clearing(_:) that nulls out the listed fields. clearing is the only way to revert a previously-set trait; merged alone can't do it. - PreviewSession.reconfigure / IOSPreviewSession.reconfigure now take an optional clearing: Set<PreviewTraits.Field> and apply both merge and clear: `self.traits = self.traits.merged(with: traits).clearing(clearing)`. - parseTraits now returns a three-tuple (traits, clearedFields, error?). clearedFields is populated by inspecting the raw MCP params for explicit empty-string values, since PreviewTraits.validated normalizes them away before the handler can see them. - handlePreviewConfigure passes the clearedFields set through to reconfigure, and considers a call "no-op" only when both traits and clearedFields are empty. - handlePreviewStart explicitly ignores clearedFields — starting a session has no existing traits to clear. New test: configureClearsTrait does a set-then-clear round trip and asserts the daemon's response summary lists colorScheme=dark after setting, and has no colorScheme= entry after clearing. Uses the summary rather than pixel diff because SwiftUI without an explicit colorScheme falls back to the OS setting, which is dark on a dark-mode Mac — so a pixel diff would spuriously pass even without the fix. All 6 ConfigureCommandTests pass; 235 total non-iOS tests still green. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Fourth PR in the CLI/MCP parity stack. Adds `previewsmcp configure` — changes rendering traits on a running preview session.
Supported traits
`--color-scheme`, `--dynamic-type-size`, `--locale`, `--layout-direction`, `--legibility-weight`.
Test plan
5 new tests in `ConfigureCommandTests`:
Regression coverage:
Stack
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