fix: address Copilot review (9 comments)

#1 GitView: hide/disable 'open in editor' for external linked worktrees
   (path outside session workspace is rejected by the fence); add
   isWithinWorkspace client helper for the gate.
#2 DiffTab: untracked diff read resolves against diff.repoRoot (child-repo
   paths are repo-root-relative, not cwd-relative); fs.read route threads
   selectedRepoOf into resolveGitPath so the host resolves the right base.
#3 GitView: chooseRepo handler mirrors chooseWorktree — clears status/
   history/log and bumps generation before async refresh, preventing stale
   rows from acting on the newly selected repository.
#4 git.ts: repoRoots/repoRoot compare roots via pathIdentity() (platform-
   aware) instead of raw includes(), fixing win32 forward/backslash
   mismatch that silently fell back to roots[0].
#5 markdown-images: mask fenced code blocks and inline code spans before
   rewriting; only rewrite reference definitions whose label is actually
   referenced by image syntax (not plain links). +3 tests.
#6 package.json: downgrade unrun ^0.3.1 → ^0.2.39 (0.3.x requires Node
   ^22.13, incompatible with declared engines >=20).
#7 market-manifest.spec: shell:true on win32 so execFileSync resolves the
   pnpm .cmd shim.
#8 smoke.spec: build html-route URL via encodeHtmlUrl() (production
   encoder) so the Windows drive separator is correct.
#9 index.ts git.worktrees route: thread selectedRepoOf so a workspace
   container's selected child repo's linked worktrees appear.

src/client/paths.ts

@@ -45,3 +45,19 @@ export function relativeTo(cwd: string, path: string): string {
   if (nPath.toLowerCase().startsWith(`${nBase.toLowerCase()}/`)) return nPath.slice(nBase.length + 1)
   return path
 }
+
+/**
+ * Whether `target` lies under `base` (or equals it), tolerant of separator
+ * style and — on Windows-style drive paths — of letter case. A client-side
+ * mirror of the host's `isWithin` (fs-tree.ts) used to decide whether a
+ * git-derived path can be opened in the editor (a linked worktree outside
+ * the session workspace cannot: the host's workspace fence would reject it).
+ */
+export function isWithinWorkspace(base: string, target: string): boolean {
+  const norm = (value: string): string => value.replace(/[\\/]+/g, '/').replace(/\/$/, '')
+  const b = norm(base)
+  const t = norm(target)
+  const lb = b.toLowerCase()
+  const lt = t.toLowerCase()
+  return lt === lb || lt.startsWith(`${lb}/`)
+}