refactor(src): narrow exception types in Phase 8 MEDIUM files (10 sites across 2 files)

Migrates the MEDIUM files (session_logger, warmup) by narrowing
the exception types from broad 'except Exception' to specific
stdlib exceptions.

session_logger.py (8 sites):
1. L99 - registry.register_session with print
   except Exception -> except (OSError, KeyError, AttributeError, TypeError)
2. L131 - registry.update_auto_whitelist_status with print
   except Exception -> except (OSError, KeyError, AttributeError, TypeError)
3. L147 - log_api_hook write/flush
   except Exception -> except (OSError, UnicodeEncodeError, ValueError)
4. L160 - log_comms json.dump
   except Exception -> except (OSError, TypeError, ValueError)
5. L188 - log_tool_call script file write
   except Exception -> except (OSError, UnicodeEncodeError)
6. L201 - log_tool_call write/flush
   except Exception -> except (OSError, UnicodeEncodeError, ValueError)
7. L226 - log_tool_output write_text
   except Exception -> except (OSError, UnicodeEncodeError)
8. L245 - log_cli_call write/flush
   except Exception -> except (OSError, TypeError, ValueError)

warmup.py (2 sites):
1. L276 - _log_canary sys.stderr.write
   except Exception -> except OSError
2. L300 - _log_summary sys.stderr.write
   except Exception -> except OSError

Decisions:
- warmup.py L85: raise RuntimeError (validation raise) - keep as-is per spec
- warmup.py L139, L215, L249: callback fires with except Exception - keep
  (user callbacks can throw anything; broad catch is correct)
- warmup.py L175: _warmup_one with except BaseException - keep
  (intentional broad catch for module import failures)

Tests verified:
- tests/test_session_logging.py (1 test) PASS
- tests/test_session_logger_reset.py (1 test) PASS
- tests/test_session_logger_optimization.py (4 tests) PASS
- tests/test_logging_e2e.py (1 test) PASS
- tests/test_warmup.py (10 tests) PASS
- tests/test_warmup_canaries.py (18 tests) PASS

src/warmup.py

@@ -273,7 +273,7 @@ class WarmupManager:
    try:
     sys.stderr.write(line)
     sys.stderr.flush()
-   except Exception: pass
+   except OSError: pass
 
  def _log_summary(self) -> None:
   if not self._log_to_stderr: return
@@ -292,12 +292,12 @@ class WarmupManager:
   if failed: parts.append(f"{failed} failed")
   if cancelled: parts.append(f"{cancelled} cancelled")
   with self._log_lock:
-   try:
-    sys.stderr.write(f"[warmup done] {total} modules: {', '.join(parts)} (sum of per-module elapsed: {total_ms:.1f}ms)\n")
-    if main_thread_violations:
-     sys.stderr.write(f"[warmup WARNING] {len(main_thread_violations)} module(s) loaded on the MAIN THREAD (violates main thread purity invariant): {', '.join(main_thread_violations)}\n")
-    sys.stderr.flush()
-   except Exception: pass
+    try:
+     sys.stderr.write(f"[warmup done] {total} modules: {', '.join(parts)} (sum of per-module elapsed: {total_ms:.1f}ms)\n")
+     if main_thread_violations:
+      sys.stderr.write(f"[warmup WARNING] {len(main_thread_violations)} module(s) loaded on the MAIN THREAD (violates main thread purity invariant): {', '.join(main_thread_violations)}\n")
+     sys.stderr.flush()
+    except OSError: pass
 
  def _snapshot(self) -> dict[str, list[str]]:
   return {