fix: fork subagents recursed forever in the Claude Code export

A fork subagent's transcript opens with a copy of the parent turn that spawned it, its own Agent call included; folding that call re-entered the same fork until RecursionError, failing every daily sync since 2026-09-24. Skip a spawn call while its own subagent is being expanded, and strip the <fork-boilerplate> preamble.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LbnmGHnFqDjyhPcCg1SEfF

CHANGELOG.md

@@ -6,6 +6,12 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## [Unreleased]
 
 ### Fixed
+- **Every scheduled Claude Code sync since 2026-09-24 died with `RecursionError`.** Claude Code's `fork` subagents write a transcript that opens with a copy of the parent turn that spawned them — the fork's own `Agent` call included. `_extract_messages` folds a subagent inline whenever it meets its spawn call, so it met that copy inside the fork, folded the same fork again, and recursed until Python's limit. One fork anywhere in `~/.claude/projects` was enough to fail the whole provider; seven existed across three sessions, and the Codex half of the run, unaffected, hid the cause behind a generic exit 1.
+
+  The recursive pass now carries the spawn ids being expanded around it and skips a tool_use whose id is among them — the enclosing subagent block already stands for that call. Because the set accumulates, a longer cycle (A spawns B, whose transcript re-spawns A) stops too. The fork's `<fork-boilerplate>` preamble — generic worker rules the harness prepends — is now stripped with the other harness tags, so a fork block opens with its actual directive.
+
+  `TestSubagentFold.test_fork_containing_its_own_spawn_call` reproduces the on-disk shape (a `fork-context-ref` record, the copied spawn call, the boilerplate-wrapped directive) and fails with the original `RecursionError` against the unfixed code. Verified against the real archive: all 85 sessions normalize, the seven forks each render as one subagent block.
+
 - **An expired Claude session key reported a raw JSON dump instead of how to fix it.** `_make_request` routed only **401** to the auth handler (`src/providers/base.py`), and claude.ai does not use 401 — an invalid or expired `sessionKey` comes back as `403 permission_error` with `details.error_code = account_session_invalid`. So the one message that names the cookie, its ~30-day lifetime and the DevTools path to refresh it could never fire for Claude. What the user got instead was the generic 4xx path: `HTTP 403 — error: {'type': 'permission_error', 'message': 'Invalid authorization'…}`, which reads like a permissions problem with the account and not like "your key expired, here is how to replace it."
 
   Measured live 2026-09-20 against `GET /api/organizations`: a valid key returns 200, while an expired key, a deliberately malformed key and **no cookie at all** return byte-identical 403s carrying that code — i.e. the API treats a dead session as an absent one. This is the same mistake as the ChatGPT media 403s below: assuming 403 means "forbidden" when the service uses it for "unauthenticated."

src/providers/claude_code.py

@@ -118,7 +118,10 @@ _HARNESS_TAG_RE = re.compile(
     r"|<command-args>.*?</command-args>"
     r"|<command-contents>.*?</command-contents>"
     r"|<local-command-stdout>.*?</local-command-stdout>"
-    r"|<system-reminder>.*?</system-reminder>",
+    r"|<system-reminder>.*?</system-reminder>"
+    # A fork subagent's first user turn: generic worker rules ahead of the
+    # fork's actual "Your directive: …", which is kept.
+    r"|<fork-boilerplate>.*?</fork-boilerplate>",
     re.DOTALL,
 )
 
@@ -530,6 +533,7 @@ def _extract_messages(
     policy: str,
     subagents: dict | None = None,
     include_sidechain: bool = False,
+    expanding: frozenset[str] = frozenset(),
 ) -> list[dict]:
     """Normalize Claude Code records into messages.
 
@@ -540,6 +544,13 @@ def _extract_messages(
     those recursive subagent passes (subagent records are flagged
     ``isSidechain``); the top-level pass keeps skipping sidechain records so a
     subagent is never also emitted as a stray top-level turn.
+
+    ``expanding`` holds the spawn ids of the subagents being folded around
+    this pass. A ``fork`` subagent's transcript opens with a copy of the parent
+    turn that spawned it, its own spawn call included; that copy is dropped,
+    since the enclosing subagent block already stands for it. Expanding it
+    again recursed without end (RecursionError, every daily sync from
+    2026-09-24).
     """
     subagents = subagents or {}
     messages: list[dict] = []
@@ -620,6 +631,8 @@ def _extract_messages(
                 elif item_type == "tool_use":
                     name = item.get("name") or "tool"
                     tool_id = item.get("id")
+                    if tool_id in expanding:
+                        continue
                     if name in _SUBAGENT_TOOL_NAMES and tool_id in subagents:
                         # A Task/Agent spawn: fold its separate transcript inline
                         # instead of collapsing it. Its own tool traffic is
@@ -633,6 +646,7 @@ def _extract_messages(
                             policy,
                             subagents,
                             include_sidechain=True,
+                            expanding=expanding | {tool_id},
                         )
                         blocks.append(
                             make_subagent_block(

tests/test_claude_code.py

@@ -370,6 +370,59 @@ class TestSubagentFold:
         ]
         assert "stray sidechain" not in top_text
 
+    def test_fork_containing_its_own_spawn_call(self, tmp_path):
+        # The shape Claude Code writes for a `fork` subagent: a context-ref
+        # record, a copy of the parent turn holding the fork's own spawn call,
+        # then the directive behind <fork-boilerplate>. Folding that copied
+        # call recursed until RecursionError.
+        fork_records = [
+            {"type": "fork-context-ref", "agentId": "a1", "parentLastUuid": "u0"},
+            {
+                "type": "assistant", "isSidechain": True,
+                "message": {"role": "assistant", "content": [
+                    {"type": "tool_use", "id": "toolu_sub1", "name": "Agent",
+                     "input": {"description": "research"}},
+                ]},
+            },
+            {
+                "type": "user", "isSidechain": True,
+                "timestamp": "2026-05-01T10:00:06.000Z",
+                "message": {"role": "user", "content": [
+                    {"type": "tool_result", "tool_use_id": "toolu_sub1",
+                     "content": [{"type": "text", "text": "Fork started"}]},
+                    {"type": "text", "text":
+                        "<fork-boilerplate>\nYou are a worker fork.\n"
+                        "</fork-boilerplate>\n\nYour directive: research X"},
+                ]},
+            },
+            {
+                "type": "assistant", "isSidechain": True,
+                "timestamp": "2026-05-01T10:00:07.000Z",
+                "message": {"role": "assistant", "content": [
+                    {"type": "text", "text": "Fork result."},
+                ]},
+            },
+        ]
+        f = _write_session(tmp_path, _parent_with_task(), name="parent-3")
+        _write_subagent(
+            f, "toolu_sub1", fork_records,
+            agent_type="fork", description="research X",
+        )
+        p = self._provider(tmp_path)
+        p.fetch_all_conversations()
+        conv = p.normalize_conversation(p.get_conversation("parent-3"))
+
+        subs = [
+            b for m in conv["messages"] for b in m["blocks"] if b["type"] == "subagent"
+        ]
+        assert len(subs) == 1
+        inner = [bb for m in subs[0]["messages"] for bb in m["blocks"]]
+        assert not any(b["type"] == "subagent" for b in inner)
+        inner_text = [b.get("text") for b in inner]
+        assert "Your directive: research X" in inner_text
+        assert "Fork result." in inner_text
+        assert not any("worker fork" in (t or "") for t in inner_text)
+
 
 # ---------------------------------------------------------------------------
 # Repo tags in title (Part C)