test(agent): pin whitespace-strip and OSError-propagation in runtime_cwd

Cover the two new hardening behaviors that were unpinned: whitespace-only
TERMINAL_CWD falling through to getcwd/None, and OSError from the getcwd
fallback arm propagating to the build_environment_hints try/except guard.

tests/agent/test_runtime_cwd.py

@@ -3,9 +3,16 @@
 import os
 from pathlib import Path
 
+import pytest
+
+import agent.runtime_cwd as rt
 from agent.runtime_cwd import resolve_agent_cwd, resolve_context_cwd
 
 
+def _raise_oserror(*args, **kwargs):
+    raise OSError("cwd gone")
+
+
 class TestResolveAgentCwd:
     def test_prefers_terminal_cwd_over_getcwd(self, monkeypatch, tmp_path):
         monkeypatch.setenv("TERMINAL_CWD", str(tmp_path))
@@ -27,6 +34,21 @@ class TestResolveAgentCwd:
         monkeypatch.setenv("TERMINAL_CWD", "~")
         assert resolve_agent_cwd() == Path(os.path.expanduser("~"))
 
+    def test_whitespace_only_terminal_cwd_falls_back_to_getcwd(self, monkeypatch, tmp_path):
+        # "   ".strip() → "" → falsy, so the launch dir wins (not a "   " path).
+        monkeypatch.setenv("TERMINAL_CWD", "   ")
+        monkeypatch.chdir(tmp_path)
+        assert resolve_agent_cwd() == tmp_path
+
+    def test_propagates_oserror_from_getcwd(self, monkeypatch):
+        # The fallback arm calls os.getcwd(), which can raise OSError (deleted cwd).
+        # The resolver must NOT swallow it — build_environment_hints owns the
+        # try/except OSError guard at the call site (prompt_builder.py:805).
+        monkeypatch.delenv("TERMINAL_CWD", raising=False)
+        monkeypatch.setattr(rt.os, "getcwd", _raise_oserror)
+        with pytest.raises(OSError):
+            resolve_agent_cwd()
+
 
 class TestResolveContextCwd:
     def test_returns_dir_when_set(self, monkeypatch, tmp_path):
@@ -49,3 +71,9 @@ class TestResolveContextCwd:
     def test_expands_leading_tilde(self, monkeypatch):
         monkeypatch.setenv("TERMINAL_CWD", "~")
         assert resolve_context_cwd() == Path(os.path.expanduser("~"))
+
+    def test_whitespace_only_terminal_cwd_returns_none(self, monkeypatch):
+        # "   ".strip() → "" → None, so the caller getcwds for discovery rather
+        # than building Path("   ") and resolving garbage under the launch dir.
+        monkeypatch.setenv("TERMINAL_CWD", "   ")
+        assert resolve_context_cwd() is None