harden(omp): resume-path test coverage, silent-fallback logging, cwd validation

Follow-up from a full-branch review pass (Opus) of the omp-mode integration:

- Add pinning tests for resolveOmpConfigForCreate() (session-routes.ts),
  exported to make it testable: the exact "resume this OMP row from
  history" pipeline that mangleOmpWorkingDir's earlier bug lived in had
  zero coverage despite being the resolver module's whole reason to exist.
- Log a warning when findLatestOmpSessionId() finds nothing on disk and
  continuation silently degrades to omp's own ambiguous --continue,
  in both call sites (session create and respawn pinning) - previously
  silent, making the degradation invisible to anyone debugging it.
- Require an absolute cwd before trusting a session file's working
  directory in omp-transcript.ts's parser, so a corrupted/malformed
  session file can't point a downstream resume at a relative or empty
  path.
- Document (don't speculatively fix) an unverified symlinked-$HOME edge
  case in mangleOmpWorkingDir(): the review's suggested realpath() fix
  assumes omp itself resolves symlinks before mangling, which is
  unconfirmed - guessing wrong there would trade one silent mismatch
  for a different one.
- Incidental: fixed unrelated pre-existing prettier drift in
  session-routes.ts (antigravity/opencode dynamic import line-wrapping)
  that was blocking the pre-commit formatting gate on this file.

Confirmed as a non-issue: the model-name regex allowing "/" is
intentional (provider/model ids like "crof/glm-5.2" were used
successfully in live testing).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/utils/omp-session-resolver.ts

@@ -37,6 +37,13 @@ const OMP_SESSION_FILE_PATTERN = /^.+_([a-zA-Z0-9-]+)\.jsonl$/;
  * Pure so it's unit-testable without touching the filesystem.
  */
 export function mangleOmpWorkingDir(workingDir: string): string {
+  // UNVERIFIED EDGE CASE: if $HOME is itself a symlink, this compares against
+  // the literal homedir() string, not a realpath()-resolved one. Whether that
+  // matches omp's own behavior is unconfirmed — we only empirically verified
+  // omp strips a literal $HOME prefix (2026-08-27), not that it canonicalizes
+  // symlinks first. Do not "fix" this with realpathSync() without confirming
+  // omp's actual behavior on a symlinked-home setup; guessing wrong here would
+  // trade one silent mismatch for a different one.
   const home = homedir();
   const relative =
     workingDir === home || workingDir.startsWith(home + sep) ? workingDir.slice(home.length) : workingDir;