Auto-assign distinct colors to split panes - #6981

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Jul 5, 2026 9:31am
cmux-staging	Building	Preview, Comment	Jul 5, 2026 9:31am

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Greptile Summary

This PR introduces terminal.autoTintSplitPanes — a setting (default on) that auto-assigns subtle, distinct background tints to terminal split panes, persists them in session snapshots, and re-applies them for remote tmux mirror panes during layout reconcile.

• Core tinting logic (TerminalSplitPaneTintPlanner) blends an 8-color palette into the true terminal background at low opacity, tracks assigned hexes to keep splits distinct, wraps deterministically after palette exhaustion, and guards against tint-of-a-tint drift by always planning against the real background color — not an already-tinted source pane.
• Persistence is gated on cmux provenance: only a live paneBackgroundOverrideColor that still equals the auto-assigned hex is written to SessionTerminalPanelSnapshot.backgroundColorHex, preventing terminal OSC/config-reload background changes from being resurrected as sticky tints on next restore.
• Localization and schema are updated across all 18 supported locales and cmux.schema.json; the terminal.autoTintSplitPanes key is wired through CmuxSettingsFileStore, KeyboardShortcutSettingsFileStore+Template, and CmuxSettingsJSONPathSupport.

Confidence Score: 5/5

Safe to merge — the feature is well-isolated, fully togglable, and the persistence provenance guard correctly prevents terminal-controlled backgrounds from leaking into session restore as cmux-assigned tints.

The tinting logic is pure computation with no mutable global state risk, the session snapshot field is optional and backward-compatible, and 11 targeted unit tests cover the planner's assignment, wrap-around, and provenance-guard behavior. The one architectural note (TerminalSplitPaneTintPlanner as a caseless enum namespace) is a style concern matching a known team rule, not a runtime defect.

Sources/Workspace.swift — contains the caseless-enum namespace and the unused static forwarder worth a follow-up cleanup.

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[newTerminalSplit called] --> B[applyAutomaticSplitPaneTints]
    B --> C{autoTintSplitPanes enabled?}
    C -- No --> Z[done]
    C -- Yes --> D[Resolve true background\nWorkspaceContentView.resolveGhosttyAppearanceConfig]
    D --> E[Collect usedHexes\nfrom all pane overrides]
    E --> F[TerminalSplitPaneTintPlanner\n.assignmentForTerminalSplit]
    F --> G{source needs tint?}
    G -- Yes --> H[nextColor → sourceColor\nadd to usedHexes + selectedHexes]
    G -- No --> I[sourceColor = nil]
    H --> J{newPane needs tint?}
    I --> J
    J -- Yes --> K[nextColor excluding selectedHexes\n→ newPaneColor]
    J -- No --> L[newPaneColor = nil]
    K --> M[Apply colors\nset autoAssignedSplitTintHex]
    L --> M

    N[Session snapshot] --> O[persistableTintHex\nliveOverride == autoAssigned?]
    O -- Yes --> P[Write backgroundColorHex]
    O -- No --> Q[Skip - terminal-controlled]

    R[Session restore] --> S{autoTintSplitPanes enabled?\n& backgroundColorHex present?}
    S -- Yes --> T[Restore paneBackgroundOverrideColor\nRe-record autoAssignedSplitTintHex]
    S -- No --> U[Skip restore]

    V[RemoteTmuxWindowMirror\nreconcile] --> W[applyAutomaticPaneTints]
    W --> X[Assign tints to untinted\nremote panes in order]

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
flowchart TD
    A[newTerminalSplit called] --> B[applyAutomaticSplitPaneTints]
    B --> C{autoTintSplitPanes enabled?}
    C -- No --> Z[done]
    C -- Yes --> D[Resolve true background\nWorkspaceContentView.resolveGhosttyAppearanceConfig]
    D --> E[Collect usedHexes\nfrom all pane overrides]
    E --> F[TerminalSplitPaneTintPlanner\n.assignmentForTerminalSplit]
    F --> G{source needs tint?}
    G -- Yes --> H[nextColor → sourceColor\nadd to usedHexes + selectedHexes]
    G -- No --> I[sourceColor = nil]
    H --> J{newPane needs tint?}
    I --> J
    J -- Yes --> K[nextColor excluding selectedHexes\n→ newPaneColor]
    J -- No --> L[newPaneColor = nil]
    K --> M[Apply colors\nset autoAssignedSplitTintHex]
    L --> M

    N[Session snapshot] --> O[persistableTintHex\nliveOverride == autoAssigned?]
    O -- Yes --> P[Write backgroundColorHex]
    O -- No --> Q[Skip - terminal-controlled]

    R[Session restore] --> S{autoTintSplitPanes enabled?\n& backgroundColorHex present?}
    S -- Yes --> T[Restore paneBackgroundOverrideColor\nRe-record autoAssignedSplitTintHex]
    S -- No --> U[Skip restore]

    V[RemoteTmuxWindowMirror\nreconcile] --> W[applyAutomaticPaneTints]
    W --> X[Assign tints to untinted\nremote panes in order]

_{Reviews (18): Last reviewed commit: "Merge remote-tracking branch 'origin/mai..." | Re-trigger Greptile}

Autoreview note — accepted v1 limitation

Automatic split-pane tints are stored in the surface's paneBackgroundOverrideColor slot, shared with Ghostty's OSC/config background overrides and carrying no provenance metadata. That single design choice has three P2 consequences flagged across autoreview passes:

1. A Ghostty config/theme reload (GHOSTTY_ACTION_CONFIG_CHANGE) clears the slot, so tints reset until the next split re-assigns them.
2. A transient OSC background set by a terminal program can be persisted into a session snapshot as if it were a cmux tint.
3. Disabling terminal.autoTintSplitPanes does not clear already-persisted tints on restore (the opt-out only affects newly created panes).

All verified real, but accepted as a v1 limitation rather than reworking the shared-slot storage now: a correct fix is source-tagging backgroundColor across the OSC handler, the config-change clear, the setter, and snapshot persist/restore — a multi-site change to the typing-latency-sensitive render path, better done as a follow-up. Documented in code at applyAutomaticSplitPaneTints (Workspace.swift).