Review follow-up to the reasoning_config cache-parity fix:
- Only inherit the parent's reasoning_config when the fork runs on the
parent's model (not routed). On the routed aux path
(auxiliary.background_review.{provider,model}) the cache is cold
regardless, so parity buys nothing, and the parent's effort vocabulary
can be invalid for the routed model/provider: OpenRouter
extra_body.reasoning.effort is forwarded unclamped
(chat_completions.py) and codex_responses only maps max/ultra for
gpt-5.6 — an exotic parent effort routed to a strict provider could
400 the review. Mirrors the existing 'not _routed' gate on
_cached_system_prompt / session_start three lines below.
- Add a routed-path regression test asserting reasoning_config is
omitted from the fork kwargs when _resolve_review_runtime returns
routed=True.
- Extract the four copy-pasted recorder stubs in
test_background_review_cache_parity.py into a single
_make_recorder_class() factory so a new fork attribute needs one stub
edit, not four.
PR #17276 painstakingly pinned `_cached_system_prompt`, `session_start`,
`session_id`, and the toolset config on the background-review fork so its
outbound request body would byte-match the parent's and hit Anthropic's
exact-prefix cache. The contributor measured a ~26% end-to-end cost
reduction on Sonnet 4.5.
That optimization is currently being silently undone by a missing
`reasoning_config` kwarg. The fork's `AIAgent(...)` call omits it, so the
fork's `reasoning_config` defaults to `None`. `anthropic_adapter.build_anthropic_kwargs`
(line ~2165) then short-circuits the `thinking` / `output_config` block,
and the fork's request body lands in a DIFFERENT Anthropic cache namespace
from the parent's.
Result on the wire: 0 `cache_read_input_tokens`, full `cache_creation_input_tokens`
of the entire parent prefix — every single background review.
7 days of midagent.db traffic from one host running stock Hermes against
Anthropic Sonnet:
```
Background-review FIRST calls (the moment a review fork is born):
count = 68
cache_write tokens = 7,004,297
cache_read tokens = 1,016,335
Cost on Sonnet ($3.75/M write vs $0.30/M read):
Spent on these writes: $26.27
Cost if they had hit parent cache instead: $2.10
WASTED: $24.16 / week / user
```
That is from one user. Multiply by Hermes's installed base for the full
impact.
Tested against api.anthropic.com directly (see refs/api-tests/ in the
attached investigation repo if needed):
| pair | cache_r | cache_w |
|---------------------------------------------|---------|---------|
| parent fresh | 0 | 24,047 |
| parent same again | 24,047 | 0 |
| fork: appends 2 new tail msgs, thinking ON | 24,047 | 22 |
| fork: appends 2 new tail msgs, thinking OFF | 0 | 24,047 |
Same fork-shape request, only difference is `thinking`. With the fix,
the fork hits the parent's full prefix and only writes the delta
(the `Review the conversation above…` prompt block, ~3-5K tokens).
One line in `agent/background_review.py`: pass
`reasoning_config=getattr(agent, "reasoning_config", None)` to the
`AIAgent(...)` constructor of the review fork. A short comment block
above it explains why so the next person who reads this code doesn't
re-introduce the regression.
`tests/run_agent/test_background_review_cache_parity.py` already covers
the system-prompt / session-id / toolset-config parity contracts that
PR #17276 introduced. I added:
* a `reasoning_config` attribute to `_make_agent_stub` so the stub has
a non-None parent value the test can verify is propagated.
* `test_review_fork_inherits_parent_reasoning_config()` — asserts the
fork's `AIAgent(...)` kwargs carry the parent's `reasoning_config`.
Pre-fix this test fails with `None vs expected {'enabled': True, 'effort': 'medium'}`;
post-fix all 4 tests in the file pass.
```
$ python -m pytest tests/run_agent/test_background_review_cache_parity.py -v
test_review_fork_inherits_parent_cached_system_prompt PASSED
test_review_fork_pins_session_start_and_session_id PASSED
test_review_fork_inherits_parent_toolset_config PASSED
test_review_fork_inherits_parent_reasoning_config PASSED ← new
```
Also runs against the broader background-review test suite:
`test_background_review.py` (4), `test_background_review_summary.py` (8),
`test_background_review_toolset_restriction.py` (3) — 19/19 pass.
`agent/curator.py:1691` has the same omission for the umbrella-curation
fork, but curator's prompt is "curate all skills" — it shares no prefix
with any user conversation, so cache-parity is a non-issue there. Worth
auditing if the curator ever takes a parent conversation as input, but
not part of this PR.
The `agent/auxiliary_client.py:1006` `reasoning_config=None` hardcode is
intentional (title/summary one-shots on short prompts — per-call cost
of namespace flip is negligible) and is also out of scope.
- Replace 18-line comment block with 3-line invariant statement
- Trim test docstrings from multi-paragraph to single-line summaries
- Trim assertion messages from 4-line to 2-line mismatch reports
- Replace 5-line WHAT comments in stubs with 1-line WHY comments
- Add ziliangdotme@gmail.com -> ziliangpeng to AUTHOR_MAP
## Summary
The background skill/memory-review fork constructed a child `AIAgent`
without propagating `enabled_toolsets` / `disabled_toolsets` from the
parent. When the parent narrowed its toolset (via `hermes tools
disable` or `config.yaml`), the fork's default `enabled_toolsets=None`
expanded to "all registered tools" — and the fork's outbound request
body sent a wider `tools[]` array than the parent's main-turn request.
Anthropic's prompt-cache key includes the `tools[]` array byte-for-byte,
so this divergence forked the cache lineage on every nudge and forced a
full prefix rewrite. On a captured ~4 hour Claude-via-Hermes session
this cost roughly 4.3 M cache-write tokens — about half of those
attributable to the per-nudge alternation between the main turn's
narrowed `tools[]` and the review fork's wider `tools[]`.
## Goal
Extend the byte-stability invariant established by PR #17276 (which
fixed `system`) to the `tools[]` slot of the request body, so the
review fork's outbound request hits the parent's warmed Anthropic
prefix cache regardless of how the parent's toolset is configured.
## Implementation
Two-line change in `agent/background_review.py`: pass
`enabled_toolsets=getattr(agent, "enabled_toolsets", None)` and the
matching `disabled_toolsets` kwarg into the `AIAgent(...)` call inside
`_spawn_background_review`. Adds an explanatory block comment that
calls out the cache-key dependency and the relationship to PR #17276.
The post-construction runtime whitelist
(`set_thread_tool_whitelist({memory, skills})`) is untouched — it
still gates which tools the model is allowed to *dispatch*. This
change aligns only what the request body *transmits*, not what the
review is allowed to do, so the safety contract from issue #15204
remains intact.
## Testing
- `tests/run_agent/test_background_review_cache_parity.py`: new
`test_review_fork_inherits_parent_toolset_config` asserts the
parent's `enabled_toolsets` and `disabled_toolsets` reach the
review-fork constructor as kwargs.
- `tests/run_agent/test_background_review_toolset_restriction.py`:
the existing `test_background_review_does_not_narrow_toolset_schema`
was inverted (its old "must NOT pass enabled_toolsets" rule was
built on the assumption that the parent always ran with the
registry default — wrong in practice when the parent is narrowed).
Renamed to `test_background_review_matches_parent_toolset_config`
and updated to assert the parent's value propagates verbatim.
- Verified the new positive test fails without the fix and passes
with it.
- Full suite for `test_background_review*`:
```
$ python -m pytest tests/run_agent/test_background_review.py \
tests/run_agent/test_background_review_summary.py \
tests/run_agent/test_background_review_toolset_restriction.py \
tests/run_agent/test_background_review_cache_parity.py -q
18 passed in 1.85s
```
## Scope
- `agent/background_review.py`: 2 added kwargs + explanatory comment.
- Two test files: one new positive test, one inverted existing test.
- No production code paths outside the review fork; no schema changes;
no public-API changes.
Refs: ziliangpeng/hermes-agent#1 (root-cause analysis with wire-level
cache-write measurements). Extends PR #17276's `system`-bytes
invariant to the `tools[]` slot.
- test_background_review_does_not_narrow_toolset_schema: review fork must
NOT pass enabled_toolsets to AIAgent (full parent schema = matching
Anthropic cache key on the 'tools' field).
- test_background_review_installs_thread_local_whitelist: the runtime
whitelist that replaces schema-level narrowing must contain memory +
skills tools and exclude terminal / send_message / delegate_task /
web_search / execute_code.
- test_review_fork_inherits_parent_cached_system_prompt: new test for
PR #17276's first root cause — the fork's _cached_system_prompt must
equal the parent's byte-for-byte.
- test_review_fork_pins_session_start_and_session_id: defensive belt-and-
suspenders for the cached-prompt inheritance.
Inverted the original test_background_review_agent_uses_restricted_toolsets
(which asserted the schema-level narrowing) — that narrowing was the
direct cause of #25322's cache miss, and the runtime whitelist replaces
its safety claim without breaking cache parity.
Refs #25322, #15204, PR #17276.
