fix(git): show changes across linked worktrees

The Git panel only ran git status against the session's own worktree,
so when DSH (or any coding agent) created a linked worktree via
'git worktree add' and modified files there, the sidebar's Git panel
stayed empty - no changed files, no diff, nothing to commit.

Enumerate all linked checkouts of the session repository and let the
user select which one the panel targets. Auto-select the dirty linked
worktree when the primary checkout is clean and exactly one linked
worktree has changes (the common DSH agent pattern). Poll status every
2s while the panel is visible so model-authored edits appear without
a manual refresh.

Security: resolveWorktree validates the client-supplied worktree path
against 'git worktree list' before using it as a git -C cwd. Uses -z
porcelain framing, which disables core.quotePath C-style quoting so
non-ASCII checkout paths round-trip losslessly.

src/client/api.ts

@@ -44,6 +44,14 @@ export interface GitStatusResult {
   entries: GitStatusEntry[]
 }
 
+/** One linked Git checkout. */
+export interface GitWorktree {
+  path: string
+  branch: string
+  current: boolean
+  changes: number
+}
+
 /** One git log row. */
 export interface GitLogEntry {
   /** Short hash (7+ chars, display). */
@@ -168,6 +176,12 @@ function scopePayload(scope: SessionScope, extra: Record<string, unknown>): Reco
   return { sessionId: scope.sessionId, ...(scope.cwd !== undefined && scope.cwd !== '' ? { cwd: scope.cwd } : {}), ...extra }
 }
 
+/** Add a linked-worktree selection to a scoped Git request. The host validates
+ * membership before using it as a command cwd. */
+function gitPayload(scope: SessionScope, worktree: string | undefined, extra: Record<string, unknown>): Record<string, unknown> {
+  return scopePayload(scope, { ...(worktree !== undefined && worktree !== '' ? { worktree } : {}), ...extra })
+}
+
 /** The sidebar API surface (session scope threaded through every call). */
 export const api = {
   sessionCwd: (scope: SessionScope, signal?: AbortSignal) =>
@@ -186,38 +200,40 @@ export const api = {
    *  `relativePath`); the host streams it under the session workspace. */
   uploadFile: (scope: SessionScope, dir: string, relativePath: string, body: Blob, signal?: AbortSignal) =>
     fetchUpload<{ path: string; size: number }>(scope, dir, relativePath, body, signal),
-  gitStatus: (scope: SessionScope, signal?: AbortSignal) =>
-    call<GitStatusResult>('git.status', scopePayload(scope, {}), signal),
-  gitDiff: (scope: SessionScope, path: string | undefined, staged: boolean, signal?: AbortSignal) =>
-    call<{ diff: string }>('git.diff', scopePayload(scope, { ...(path !== undefined ? { path } : {}), staged }), signal),
-  gitStage: (scope: SessionScope, path?: string) =>
-    call<{ ok: true }>('git.stage', scopePayload(scope, { ...(path !== undefined ? { path } : {}) })),
-  gitUnstage: (scope: SessionScope, path?: string) =>
-    call<{ ok: true }>('git.unstage', scopePayload(scope, { ...(path !== undefined ? { path } : {}) })),
-  gitCommit: (scope: SessionScope, message: string) =>
-    call<{ ok: true }>('git.commit', scopePayload(scope, { message })),
-  gitBranch: (scope: SessionScope, signal?: AbortSignal) =>
-    call<{ current: string; names: string[] }>('git.branch', scopePayload(scope, {}), signal),
-  gitCheckout: (scope: SessionScope, branch: string) =>
-    call<{ ok: true }>('git.checkout', scopePayload(scope, { branch })),
+  gitWorktrees: (scope: SessionScope, signal?: AbortSignal) =>
+    call<GitWorktree[]>('git.worktrees', scopePayload(scope, {}), signal),
+  gitStatus: (scope: SessionScope, worktree?: string, signal?: AbortSignal) =>
+    call<GitStatusResult>('git.status', gitPayload(scope, worktree, {}), signal),
+  gitDiff: (scope: SessionScope, path: string | undefined, staged: boolean, worktree?: string, signal?: AbortSignal) =>
+    call<{ diff: string }>('git.diff', gitPayload(scope, worktree, { ...(path !== undefined ? { path } : {}), staged }), signal),
+  gitStage: (scope: SessionScope, path?: string, worktree?: string) =>
+    call<{ ok: true }>('git.stage', gitPayload(scope, worktree, { ...(path !== undefined ? { path } : {}) })),
+  gitUnstage: (scope: SessionScope, path?: string, worktree?: string) =>
+    call<{ ok: true }>('git.unstage', gitPayload(scope, worktree, { ...(path !== undefined ? { path } : {}) })),
+  gitCommit: (scope: SessionScope, message: string, worktree?: string) =>
+    call<{ ok: true }>('git.commit', gitPayload(scope, worktree, { message })),
+  gitBranch: (scope: SessionScope, worktree?: string, signal?: AbortSignal) =>
+    call<{ current: string; names: string[] }>('git.branch', gitPayload(scope, worktree, {}), signal),
+  gitCheckout: (scope: SessionScope, branch: string, worktree?: string) =>
+    call<{ ok: true }>('git.checkout', gitPayload(scope, worktree, { branch })),
   /** Recent commit history, lazily pageable (skip/count; defaults 0/30). */
-  gitLog: (scope: SessionScope, count?: number, skip?: number, signal?: AbortSignal) =>
-    call<GitLogEntry[]>('git.log', scopePayload(scope, {
+  gitLog: (scope: SessionScope, count?: number, skip?: number, worktree?: string, signal?: AbortSignal) =>
+    call<GitLogEntry[]>('git.log', gitPayload(scope, worktree, {
       ...(count !== undefined ? { count } : {}),
       ...(skip !== undefined ? { skip } : {}),
     }), signal),
   /** Full patch text of one commit (diff display for the history rows). */
-  gitCommitDiff: (scope: SessionScope, hash: string, signal?: AbortSignal) =>
-    call<{ diff: string }>('git.commit-diff', scopePayload(scope, { hash }), signal),
+  gitCommitDiff: (scope: SessionScope, hash: string, worktree?: string, signal?: AbortSignal) =>
+    call<{ diff: string }>('git.commit-diff', gitPayload(scope, worktree, { hash }), signal),
   /** Discard the worktree changes of one file (the index is untouched). */
-  gitDiscard: (scope: SessionScope, path: string) =>
-    call<{ ok: true }>('git.discard', scopePayload(scope, { path })),
+  gitDiscard: (scope: SessionScope, path: string, worktree?: string) =>
+    call<{ ok: true }>('git.discard', gitPayload(scope, worktree, { path })),
   /** Revert one commit onto the current branch. */
-  gitRevert: (scope: SessionScope, hash: string) =>
-    call<{ ok: true }>('git.revert', scopePayload(scope, { hash })),
+  gitRevert: (scope: SessionScope, hash: string, worktree?: string) =>
+    call<{ ok: true }>('git.revert', gitPayload(scope, worktree, { hash })),
   /** Cherry-pick one commit onto the current branch. */
-  gitCherryPick: (scope: SessionScope, hash: string) =>
-    call<{ ok: true }>('git.cherry-pick', scopePayload(scope, { hash })),
+  gitCherryPick: (scope: SessionScope, hash: string, worktree?: string) =>
+    call<{ ok: true }>('git.cherry-pick', gitPayload(scope, worktree, { hash })),
   /** Release a terminal's process immediately (tab closed; the WS close frame
    *  may be unreachable while the socket is down, so the host also accepts
    *  this explicit route). */