🤖 fix: persist runtimeConfig when forking local workspaces

[ammar-agent]

Summary

Fix local workspace fork creating corrupt worktree workspaces by persisting runtimeConfig in config.addWorkspace(), then simplify the codebase by removing redundant inline fallbacks.

Background

PR #1721 (commit 4238ff4) added fork support for local (project-dir) workspaces. The LocalRuntime.forkWorkspace() was correctly implemented to return the project path, and workspaceService.fork() correctly assembled the FrontendWorkspaceMetadata with runtimeConfig: forkedRuntimeConfig.

However, when config.addWorkspace() stored the forked workspace entry, it discarded the runtimeConfig field:

const workspaceEntry: Workspace = {
  path: workspacePath,
  id: metadata.id,
  name: metadata.name,
  createdAt: metadata.createdAt,
  // runtimeConfig was missing!
};

On subsequent config loads, getAllWorkspaceMetadata() would see no runtimeConfig and apply DEFAULT_RUNTIME_CONFIG (type: "worktree" with srcBaseDir), causing the forked workspace to be treated as a worktree runtime. This created "corrupt worktree" errors because WorktreeRuntime operations would fail on directories that were never set up as git worktrees.

Implementation

Commit 1: Fix runtimeConfig persistence

One-line fix: include runtimeConfig: metadata.runtimeConfig in the workspace entry when calling addWorkspace().

Commit 2: Remove redundant fallbacks

The config layer already guarantees every WorkspaceMetadata has a runtimeConfig (via DEFAULT_RUNTIME_CONFIG applied in getAllWorkspaceMetadata()). This commit removes 13 inline ?? { type: "local", srcBaseDir } fallbacks across 5 service files that were:

• Redundant: The metadata type already includes runtimeConfig
• Inconsistent: Inline fallbacks used type: "local" while the canonical default is type: "worktree"
• Bug-masking: Silently substituting values instead of surfacing issues

Files cleaned up:

• workspaceService.ts (5 locations)
• agentSession.ts (5 locations)
• aiService.ts, terminalService.ts, workspaceMcpOverridesService.ts (1 each)

Commit 3: Fix namedWorkspacePath persistence (Codex review feedback)

config.addWorkspace() was hardcoding worktree-style paths (~/.mux/src/...) even for local workspaces. After app restart, this caused Open-in-Editor and path display to use the wrong directory.

Fix: use namedWorkspacePath from the metadata if provided (which is computed runtime-aware by Runtime.getWorkspacePath()), falling back to worktree-style path only for legacy callers.

Validation

• Integration tests for fork persistence:
  • Creates local workspace → forks → verifies runtimeConfig survives reload
  • Verifies namedWorkspacePath is the project path (not ~/.mux/src/...) after reload
• make typecheck passes
• make static-check passes
• TEST_INTEGRATION=1 bun x jest tests/ipc/forkWorkspace.test.ts - all 9 tests pass

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Generated with mux · Model: anthropic:claude-sonnet-4-20250514

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