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/DiffTab.tsx

@@ -61,7 +61,10 @@ export function DiffTab(props: { sessionId: string; cwd: string | undefined; dif
         // Empty diff: an untracked file (git diff never lists it) falls back
         // to a full-file addition; anything else is a genuine no-text-change.
         if (diff.untracked === true && !diff.staged) {
-          const text = await api.fsRead(scope, resolveSidebarPath(diff.worktree ?? cwd, diff.path))
+          // A child-repo path is relative to diff.repoRoot, not the session
+          // cwd or the linked-worktree root; resolve against whichever the
+          // diff ref carries so the untracked fallback reads the right file.
+          const text = await api.fsRead(scope, resolveSidebarPath(diff.repoRoot ?? diff.worktree ?? cwd, diff.path))
           if (!cancelled) {
             setData(text.kind === 'text' ? { diff: '', untracked: text.content } : { diff: '' })
           }