linux(socket): implement workspace.action (rename, pin, color, move, close_*)

[Jesssullivan]

Summary

Implements workspace.action on the Linux daemon, mirroring the macOS v2WorkspaceAction dispatcher. Supports 12 sub-actions:

• Mutation: rename, clear_name, pin, unpin, set_color, clear_color
• Ordering: move_up, move_down, move_top
• Bulk close: close_above, close_below, close_others

Recognized macOS actions with no Linux backing field yet (set_description, clear_description, mark_read, mark_unread) return a structured \"action not implemented on linux\" error so callers can detect parity gaps. Unknown actions return \"unsupported action\" with a supported allowlist.

The close_* variants pre-compute the target ID set before mutation so the per-close index shift in tab_manager.closeWorkspace cannot corrupt iteration. Pinned workspaces are skipped — matching macOS semantics.

Adds a pure socket round-trip test (tests_v2/test_workspace_action.py) exercising every supported action, both error paths, and the focused-workspace fallback when no workspace_id is provided. The test pins baseline workspaces before invoking close_* so it cannot disturb workspaces it didn't create, and cleans up by unpinning + closing what it touched.

Refs: cmux issue #220 (Phase 3 Sprint A item 1).

Test plan

• Socket Tests (Self-Hosted Linux) workflow passes on this branch
• tests_v2/test_workspace_action.py is discovered by scripts/run-socket-tests.sh (matches no exclusion pattern)
• No regression in test_surface_action_rename.py (PR linux(socket): implement surface.action / tab.action (rename, pin, mark_read) #218) or test_workspace_reorder.py

[greptile-apps]

Greptile Summary

This PR implements workspace.action on the Linux daemon, mirroring the macOS v2WorkspaceAction dispatcher with 12 sub-actions (mutation, reorder, and bulk close). The JSON-injection issue flagged in a previous review is correctly addressed with writeJsonString throughout. The pre-computed ID-snapshot approach for close_* correctly handles the index-shift problem caused by sequential closeWorkspace calls.

One concern from a previous review thread remains open: the catch break in the close_* collection loop silently truncates the target set on alloc failure, producing a partial mutation with no indication to the caller.

Confidence Score: 4/5

Safe to merge with one known open concern from a prior review thread.

JSON injection (previously flagged P1) is correctly resolved with writeJsonString. Implementation logic for all 12 actions is sound: insertAssumeCapacity is safe after orderedRemove, ws pointer remains valid because the list stores Workspace pointers, and close_ pre-computation correctly handles index shifts. The catch break silent-truncation issue (flagged in a previous thread) remains unaddressed — a partial close mutation still returns "closed":N with no error signal — which keeps the score at 4 rather than 5.

cmux-linux/src/socket.zig — close_* collection loop catch break

Important Files Changed

Filename	Overview
cmux-linux/src/socket.zig	Adds handleWorkspaceAction with 12 sub-actions; JSON injection correctly guarded with writeJsonString; catch break on alloc failure (flagged previously) still present in close_* collection loop.
tests_v2/test_workspace_action.py	Comprehensive pure socket round-trip test; covers all 12 actions, both error paths, and focused-workspace fallback; baseline workspaces pinned before close_* to prevent test pollution; cleanup handled in finally.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[workspace.action request] --> B{action param?}
    B -- missing --> ERR1[error: missing action]
    B -- present --> C{workspace_id param?}
    C -- present --> D[findWorkspaceById]
    C -- absent --> E[tm.selected_index fallback]
    D -- not found --> ERR2[error: workspace not found]
    D -- found --> F{dispatch on action}
    E -- no selection --> ERR3[error: no workspace]
    E -- found --> F
    F -- rename --> G[dupe title, free old, updateTabTitle\nwriteJsonString response]
    F -- clear_name --> H[free old title, updateTabTitle]
    F -- pin/unpin --> I[set is_pinned, sidebar refresh]
    F -- set_color --> J[dupe color, free old\nwriteJsonString response]
    F -- clear_color --> K[free old color, sidebar refresh]
    F -- move_up --> L[orderedRemove + insertAssumeCapacity idx-1\nre-scan for new index]
    F -- move_down --> M[orderedRemove + insertAssumeCapacity idx+1\nre-scan for new index]
    F -- move_top --> N[orderedRemove + insertAssumeCapacity 0\nindex always 0]
    F -- close_above/below/others --> O[pre-compute target IDs\nskip pinned + operator]
    O --> P[close each by re-finding ID\nafter each index shift]
    P --> Q[writeJsonString response with closed count]
    F -- set_description/clear_description/mark_read/mark_unread --> R[error: not implemented on linux]
    F -- unknown --> S[error: unsupported action\nwith supported list]

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_{Reviews (3): Last reviewed commit: "linux(socket): name WorkspaceLookup so p..." | Re-trigger Greptile}

[Jesssullivan]

Preemptively addressed the same two patterns Greptile flagged on the sibling surface.action PR (#218):

• Alloc-then-free reorder: rename and set_color now allocate the new value first, then free the old, then assign. No more use-after-free on dupe failure.
• JSON injection: title, color, and action echoes (including the close_*, unimplemented, and unsupported error envelopes) all use writeJsonString to escape user input. The JSON envelope cannot be broken by a value containing ", \\, or control characters.

Commit: 3b0b92a.