fix(issue-25): a relative --plan-file is taken against the control root, as its usage line says

Review R1/N1 (reviewer-grok-01, planner-reviewer-codex-01), reproduced before
fixing. The usage line and SKILL.md both promise "relative to the control
root", but parse_args did Path(...).expanduser().resolve(), which is relative
to the caller's cwd. The runner never chdirs to workspace_root, so the two are
routinely different - the documented recipe runs the loop from the control root
while the source root is a worktree.

Two ways it went wrong: a plan that exists only under the control root was not
found at all (exit 1), and a same-named file in the caller's cwd was loaded
instead, quietly putting an unrelated plan into the first implementation
prompt. That second one is the very failure #25 is about, reintroduced through
the option meant to replace it.

Resolve against workspace_root the way jobs_dir already does (Issue #21 R2);
pathlib's `/` leaves an absolute or expanded-home path untouched. Every earlier
test passed an absolute tmp_path, which is why none of them caught this: P3c
covers both failure modes with the control root away from the caller's cwd, and
P3d pins that absolute and ~ paths are not rewritten.

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

.agents/skills/lib_py/loop/runner.py

@@ -256,7 +256,12 @@ class LoopRunner:
                 print("Use --plan to have the Planner write a new plan, or --plan-file to reuse one:", file=sys.stderr)
                 print('  run_loop.sh --creator <creator> --plan-file <path> --task "..."', file=sys.stderr)
                 sys.exit(1)
-            resolved = Path(self.plan_file).expanduser().resolve()
+            # A relative path is taken against the control root, as the usage
+            # line says and as jobs_dir already does (Issue #21 R2): the runner
+            # never chdirs to workspace_root, so resolving against the caller's
+            # cwd would look somewhere else entirely - and could find a
+            # same-named file there. `/` keeps an absolute path as it is.
+            resolved = (self.workspace_root / Path(self.plan_file).expanduser()).resolve()
             text = self._plan_text(resolved)
             if text is None:
                 log_error(f"--plan-file {resolved}: not a readable file with plan text in it.")