Bound a call that never reads and restore the iteration test

The read deadline only gets control at a read, so code that computes without
reading escaped it. Give the pool a request_timeout above code_timeout. The
watchdog kills the worker, and execute() already replaces a dead session, so a
runaway call fails and the next call recovers. A read refusal keeps the
variables, so it has to win the race whenever code does read.

Restore test_open_file_objects_are_not_iterable. Replacing the neighbouring
write test by text range deleted it, which left the instructions carrying a
prohibition with nothing to signal when monty lifts it.

Reuse the VFS and the pool when a session is replaced, so recovery skips the
document scan. Mount metadata.json with a lambda rather than a factory. Cover
open() in write mode. Fold the crash entry into the pydantic-monty bullet,
because no release shipped the worker without it.

CHANGELOG.md

@@ -8,7 +8,7 @@
 ### Changed
 
 - Require `pydantic-ai-slim>=2.18,<3`.
-- `pydantic-monty` bumped to `>=0.0.19`; sandbox code now runs in a subprocess worker pool.
+- `pydantic-monty` bumped to `>=0.0.19`; sandbox code now runs in a subprocess worker pool. A crashed or timed-out worker fails one call and the next call gets a replacement session.
 - The analysis sandbox gives Monty a duration budget of `analysis.code_timeout * analysis.max_executions` for the session, was `analysis.code_timeout`.
 - `enable_thinking` maps onto Pydantic AI's unified `thinking` setting for the `anthropic`, `gemini`, `groq` and `bedrock` providers. The Anthropic thinking budget is now Pydantic AI's default of 10000 tokens, was 4096, and `max_tokens` must exceed it on budget-based Claude models; `enable_thinking: false` disables Gemini thinking rather than only hiding thoughts; Groq maps reasoning effort rather than `groq_reasoning_format`; Bedrock Qwen with `enable_thinking: false` no longer sends `reasoning_config`, while Bedrock-served Claude keeps an explicit `thinking: disabled`. The `openai` and `ollama` providers still map to `openai_reasoning_effort`.
 - `provider: bedrock` with a proprietary OpenAI model such as `openai.o3-mini-v1:0` raises `UserError`: Bedrock Converse serves only the `gpt-oss` family. Use `provider: bedrock-mantle`.
@@ -22,7 +22,6 @@
 - `docs/installation.md` documents the `jina`, `s3` and `ingester` extras, names the extras the full package actually pulls, drops the removed MixedBread AI reranker, and no longer lists Anthropic as a built-in provider.
 - `docs/tuning.md` no longer points at the removed `claim_timeout_s` setting.
 - `analysis.code_timeout` is checked before each document read; code that reads in a loop no longer overruns it by the duration of the outstanding reads.
-- A crashed Monty worker no longer poisons the analysis sandbox for the rest of the run: `execute` reports the crash and the next call checks out a replacement session.
 - `metadata.json` in the document VFS rejects writes, matching `content.txt`, `items.jsonl` and `toc.json`.
 
 ### Removed

haiku_rag_slim/haiku/rag/sandbox/sandbox.py

@@ -28,6 +28,10 @@ if TYPE_CHECKING:
     from haiku.rag.client import HaikuRAG
 
 
+_REQUEST_TIMEOUT_MARGIN_S = 30.0
+"""Grace above ``code_timeout`` before the pool watchdog kills the worker."""
+
+
 @dataclass
 class SandboxResult:
     """Result of executing code in the sandbox."""
@@ -417,20 +421,11 @@ class Sandbox:
             )
 
             # A MemoryFile accepts writes, so mount metadata.json through the
-            # same read/deny pair as the rest. The content is already built,
-            # so the reader stays eager.
-            def _make_metadata_reader(
-                text: str,
-            ) -> Callable[["PurePosixPath"], str]:
-                def read_metadata(_path: "PurePosixPath") -> str:
-                    return text
-
-                return read_metadata
-
+            # same read and deny pair as the rest. The content is already built.
             files.append(
                 CallbackFile(
                     f"{doc_dir}/metadata.json",
-                    read=_make_metadata_reader(metadata),
+                    read=lambda _path, text=metadata: text,
                     write=_deny_write,
                 )
             )
@@ -476,6 +471,17 @@ class Sandbox:
 
         return OSAccess(files)
 
+    def _request_timeout(self) -> float:
+        """Hard per-call deadline for the pool watchdog.
+
+        The read deadline refuses the next read at ``code_timeout`` and keeps the
+        session, so it wins for code that reads. This watchdog is the fallback
+        for code that computes without reading: it kills the worker, which loses
+        the variables the session held. Leave room for one read that is already
+        in flight, so the graceful refusal wins the race.
+        """
+        return self._config.analysis.code_timeout + _REQUEST_TIMEOUT_MARGIN_S
+
     def _session_limits(self) -> ResourceLimits:
         """Resource limits for the worker session.
 
@@ -491,10 +497,13 @@ class Sandbox:
 
     async def _ensure_initialized(self) -> tuple[AsyncMontySession, OSAccess]:
         """Check out a worker session and build the VFS on first use."""
-        if self._session is None:
+        if self._vfs is None:
             self._vfs = await self._build_vfs()
-            self._pool = AsyncMonty()
-            await self._pool.__aenter__()
+        if self._pool is None:
+            pool = AsyncMonty(request_timeout=self._request_timeout())
+            await pool.__aenter__()
+            self._pool = pool
+        if self._session is None:
             session = self._pool.checkout(limits=self._session_limits())
             await session.__aenter__()
             self._session = session

tests/sandbox/test_sandbox.py

@@ -471,6 +471,88 @@ class TestSandboxVFS:
         finally:
             await sb.close()
 
+    @pytest.mark.asyncio
+    async def test_open_for_writing_is_denied(self, temp_db_path):
+        """`open()` in write mode is refused, not only `Path.write_text`."""
+        from docling_core.types.doc.document import DoclingDocument
+        from docling_core.types.doc.labels import DocItemLabel
+
+        config = AppConfig()
+        docling = DoclingDocument(name="d")
+        docling.add_text(label=DocItemLabel.TEXT, text="Foxes and dogs.")
+
+        async with HaikuRAG(temp_db_path, create=True) as client:
+            doc = await client.import_document(
+                docling,
+                [
+                    Chunk(
+                        content="Foxes and dogs.",
+                        embedding=[0.1] * config.embeddings.model.vector_dim,
+                        order=0,
+                    )
+                ],
+                uri="test://openwrite",
+            )
+
+        sb = Sandbox(db_path=temp_db_path, config=config, context=AnalysisContext())
+        try:
+            result = await sb.execute(
+                "try:\n"
+                f"    with open('/documents/{doc.id}/content.txt', 'w') as f:\n"
+                "        f.write('nope')\n"
+                "    print('WROTE')\n"
+                "except PermissionError:\n"
+                "    print('DENIED')"
+            )
+            assert result.success, result.stderr
+            assert "DENIED" in result.stdout
+            assert "WROTE" not in result.stdout
+        finally:
+            await sb.close()
+
+    @pytest.mark.asyncio
+    async def test_open_file_objects_are_not_iterable(self, temp_db_path):
+        """Pins the limitation the instructions warn about: pydantic/monty#490.
+
+        A failure here means Monty gained iteration support and the
+        `for line in f` prohibition in the analysis instructions is now wrong.
+        """
+        from docling_core.types.doc.document import DoclingDocument
+        from docling_core.types.doc.labels import DocItemLabel
+
+        config = AppConfig()
+        docling = DoclingDocument(name="d")
+        docling.add_text(label=DocItemLabel.TEXT, text="one\ntwo")
+
+        async with HaikuRAG(temp_db_path, create=True) as client:
+            doc = await client.import_document(
+                docling,
+                [
+                    Chunk(
+                        content="one\ntwo",
+                        embedding=[0.1] * config.embeddings.model.vector_dim,
+                        order=0,
+                    )
+                ],
+                uri="test://lines",
+            )
+
+        sb = Sandbox(db_path=temp_db_path, config=config, context=AnalysisContext())
+        try:
+            result = await sb.execute(
+                f"for line in open('/documents/{doc.id}/content.txt'):\n    print(line)"
+            )
+            assert result.success is False
+            assert "not iterable" in result.stderr
+
+            # The documented alternatives do work.
+            result = await sb.execute(
+                f"print(len(open('/documents/{doc.id}/content.txt').readlines()))"
+            )
+            assert result.success, result.stderr
+        finally:
+            await sb.close()
+
     @pytest.mark.asyncio
     @pytest.mark.vcr()
     async def test_context_filter_limits_vfs(self, temp_db_path):
@@ -819,3 +901,39 @@ class TestSandboxWorkerCrash:
             assert lost.success is False
         finally:
             await sb.close()
+
+
+class TestSandboxRequestTimeout:
+    """The pool watchdog bounds a call that never reads."""
+
+    def test_request_timeout_sits_above_the_read_deadline(self, temp_db_path):
+        """A read refusal keeps the session, so it must win the race."""
+        config = AppConfig()
+        config.analysis.code_timeout = 5.0
+        sb = Sandbox(db_path=temp_db_path, config=config, context=AnalysisContext())
+
+        assert sb._request_timeout() > config.analysis.code_timeout
+
+    @pytest.mark.asyncio
+    async def test_runaway_compute_is_killed_and_the_next_call_recovers(
+        self, temp_db_path, monkeypatch
+    ):
+        """Code that never reads escapes the read deadline. The watchdog kills it."""
+        config = AppConfig()
+        async with HaikuRAG(temp_db_path, create=True):
+            pass
+
+        sb = Sandbox(db_path=temp_db_path, config=config, context=AnalysisContext())
+        monkeypatch.setattr(sb, "_request_timeout", lambda: 1.0)
+        try:
+            runaway = await sb.execute(
+                "x = 0\nfor i in range(500000000):\n    x += i\nprint(x)"
+            )
+            assert runaway.success is False
+            assert "restarted" in runaway.stderr
+
+            recovered = await sb.execute("print('alive')")
+            assert recovered.success, recovered.stderr
+            assert "alive" in recovered.stdout
+        finally:
+            await sb.close()