[eric] client-pool: stop hashing the compaction cutoff, it respawned the CLI every turn past 65% context

backend/apps/agents/manager/run/client_pool.py

@@ -40,11 +40,16 @@ p_last_field_digests: Dict[str, Dict[str, str]] = {}
 def boot_fingerprint(options_kwargs: Dict, session: AgentSession) -> str:
     """Hash of every input the CLI subprocess freezes at boot. Includes the full mcp_servers config
     (so MCPActivate / model-env changes respawn), the composed system prompt (so per-turn selection
-    context respawns instead of silently not applying), branch, and the compaction cutoff (else a
-    live client would keep the untrimmed transcript forever)."""
+    context respawns instead of silently not applying), and the branch.
+
+    The compaction cutoff is deliberately NOT hashed. It only ever changes prompt_content (the
+    rebuilt history prefix), which is sent per query, never frozen at boot, and on the resume path
+    the CLI replays its own untrimmed transcript regardless. Every path that does rebuild history
+    (needs_fresh_session / needs_fork / fork) already forces a respawn through force_respawn. Hashing
+    it bought nothing and cost a full CLI respawn on EVERY turn once a session crossed
+    compact_threshold_pct, measured at +1.0s TTFT per turn."""
     frozen = {k: v for k, v in options_kwargs.items() if k not in P_NON_BOOT_KEYS}
     frozen["p_branch"] = session.active_branch_id
-    frozen["p_compacted_through"] = session.compacted_through_msg_id
     # Pool diagnostics (OPENSWARM_POOL_DIAG=1): on a respawn, names WHICH boot field drifted; the tool for debugging respawn churn (e.g. the thinking short/long-prompt flip) in the field.
     if os.environ.get("OPENSWARM_POOL_DIAG") == "1":
         digests = {k: hashlib.sha256(json.dumps(v, sort_keys=True, default=str).encode()).hexdigest()[:10] for k, v in frozen.items()}

backend/tests/test_boot_fingerprint.py

@@ -0,0 +1,67 @@
+"""What the client pool's boot fingerprint does and does NOT hash.
+
+Reuse is gated on this hash, so anything the CLI subprocess freezes at boot must be in it (a stale
+live client is the bug it exists to prevent), and anything sent per query must be out of it (hashing
+those respawns the CLI for nothing, which is exactly what the compaction cutoff used to do)."""
+
+import pytest
+
+from backend.apps.agents.core.models import AgentSession
+from backend.apps.agents.manager.run.client_pool import boot_fingerprint
+
+BASE_KWARGS = {
+    "model": "haiku",
+    "cwd": "/tmp/ws",
+    "system_prompt": {"type": "preset", "preset": "claude_code"},
+    "allowed_tools": ["Read"],
+    "disallowed_tools": ["mcp__claude_ai_*"],
+    "mcp_servers": {"openswarm-mcp-meta": {"command": "python", "args": ["m.py"], "type": "stdio"}},
+    "can_use_tool": lambda: None,
+    "stderr": lambda line: None,
+    "hooks": {"PreToolUse": []},
+}
+
+
+def make_session() -> AgentSession:
+    return AgentSession(name="t", model="haiku", mode="agent")
+
+
+def test_fingerprint_stable_across_per_turn_keys():
+    s = make_session()
+    a = boot_fingerprint(dict(BASE_KWARGS), s)
+    changed = dict(BASE_KWARGS)
+    changed["can_use_tool"] = lambda: 1
+    changed["stderr"] = lambda line: 1
+    changed["hooks"] = {"PreToolUse": ["different"]}
+    changed["resume"] = "sdk-session-xyz"
+    changed["fork_session"] = True
+    assert boot_fingerprint(changed, s) == a
+
+
+def test_fingerprint_ignores_the_compaction_cutoff():
+    """The cutoff only rewrites prompt_content, which is sent per query and never frozen at boot,
+    and every path that rebuilds history already forces a respawn. Hashing it respawned the CLI on
+    every turn past compact_threshold_pct for zero token saving (+1.0s TTFT per turn, measured)."""
+    s = make_session()
+    before = boot_fingerprint(dict(BASE_KWARGS), s)
+    for cutoff in ("msg42", "msg43", "msg44"):
+        s.compacted_through_msg_id = cutoff
+        assert boot_fingerprint(dict(BASE_KWARGS), s) == before
+
+
+@pytest.mark.parametrize("mutate", [
+    lambda k, s: k.__setitem__("mcp_servers", {**k["mcp_servers"], "x": {"command": "node", "type": "stdio"}}),
+    lambda k, s: k.__setitem__("system_prompt", {"type": "preset", "preset": "claude_code", "append": "sel"}),
+    lambda k, s: k.__setitem__("model", "gpt-5-mini"),
+    lambda k, s: k.__setitem__("cwd", "/tmp/other"),
+    lambda k, s: k.__setitem__("allowed_tools", ["Read", "Bash"]),
+    lambda k, s: k.__setitem__("tools", ["Read", "Bash", "ToolSearch"]),
+    lambda k, s: setattr(s, "active_branch_id", "branch2"),
+])
+def test_fingerprint_changes_on_boot_inputs(mutate):
+    s = make_session()
+    kwargs = dict(BASE_KWARGS)
+    kwargs["mcp_servers"] = dict(BASE_KWARGS["mcp_servers"])
+    before = boot_fingerprint(kwargs, s)
+    mutate(kwargs, s)
+    assert boot_fingerprint(kwargs, s) != before

backend/tests/test_client_pool.py

@@ -1,19 +1,16 @@
 """Invariant + seeded-simulation tests for the persistent-client pool (lever A of the TTFT work).
-Proves the red-teamed safety properties hold by construction: fingerprint-gated reuse, respawn on
-any boot-input change, pop-first disposal, never-raising teardown, and (seeded sim) that random op
-sequences never reuse a stale client, never double-boot needlessly, and always recover a dead one."""
+Proves the red-teamed safety properties hold by construction: fingerprint-gated reuse, pop-first
+disposal, never-raising teardown, idle/LRU reclaim, and (seeded sim) that random op sequences never
+reuse a stale client, never double-boot needlessly, and always recover a dead one. What the
+fingerprint itself hashes lives in test_boot_fingerprint.py."""
 
 import asyncio
 import random
 from typing import Dict, List
 
-import pytest
-
-from backend.apps.agents.core.models import AgentSession
 from backend.apps.agents.manager.run.client_pool import (
     ClientHandle,
     acquire_client,
-    boot_fingerprint,
     dispose_all_clients,
     dispose_client,
     dispose_client_soon,
@@ -39,56 +36,6 @@ class FakeClient:
             raise RuntimeError("teardown boom")
 
 
-def make_session(branch: str = "main", compacted: str | None = None) -> AgentSession:
-    s = AgentSession(name="t", model="haiku", mode="agent")
-    s.active_branch_id = branch
-    s.compacted_through_msg_id = compacted
-    return s
-
-
-BASE_KWARGS = {
-    "model": "haiku",
-    "cwd": "/tmp/ws",
-    "system_prompt": {"type": "preset", "preset": "claude_code"},
-    "allowed_tools": ["Read"],
-    "disallowed_tools": ["mcp__claude_ai_*"],
-    "mcp_servers": {"openswarm-mcp-meta": {"command": "python", "args": ["m.py"], "type": "stdio"}},
-    "can_use_tool": lambda: None,
-    "stderr": lambda line: None,
-    "hooks": {"PreToolUse": []},
-}
-
-
-def test_fingerprint_stable_across_per_turn_keys():
-    s = make_session()
-    a = boot_fingerprint(dict(BASE_KWARGS), s)
-    changed = dict(BASE_KWARGS)
-    changed["can_use_tool"] = lambda: 1
-    changed["stderr"] = lambda line: 1
-    changed["hooks"] = {"PreToolUse": ["different"]}
-    changed["resume"] = "sdk-session-xyz"
-    changed["fork_session"] = True
-    assert boot_fingerprint(changed, s) == a
-
-
-@pytest.mark.parametrize("mutate", [
-    lambda k, s: k.__setitem__("mcp_servers", {**k["mcp_servers"], "x": {"command": "node", "type": "stdio"}}),
-    lambda k, s: k.__setitem__("system_prompt", {"type": "preset", "preset": "claude_code", "append": "sel"}),
-    lambda k, s: k.__setitem__("model", "gpt-5-mini"),
-    lambda k, s: k.__setitem__("cwd", "/tmp/other"),
-    lambda k, s: k.__setitem__("allowed_tools", ["Read", "Bash"]),
-    lambda k, s: setattr(s, "active_branch_id", "branch2"),
-    lambda k, s: setattr(s, "compacted_through_msg_id", "msg42"),
-])
-def test_fingerprint_changes_on_boot_inputs(mutate):
-    s = make_session()
-    kwargs = dict(BASE_KWARGS)
-    kwargs["mcp_servers"] = dict(BASE_KWARGS["mcp_servers"])
-    before = boot_fingerprint(kwargs, s)
-    mutate(kwargs, s)
-    assert boot_fingerprint(kwargs, s) != before
-
-
 def test_reuse_respawn_force_and_teardown():
     async def run():
         pool: Dict[str, ClientHandle] = {}