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## Description
`TrafficLearner` (the memory/learning subsystem that accumulates
patterns from proxy traffic) has an unbounded in-memory accumulator.
`_pattern_counts` maps `content_hash -> (pattern, count)`. A pattern is
added on first sighting, its count is bumped on each re-sighting, and it
is **removed only when it reaches `min_evidence`** (default 5), at which
point it is promoted and its hash moves to `_saved_hashes`:
```python
if h in self._pattern_counts:
existing, count = self._pattern_counts[h]
count += 1
self._pattern_counts[h] = (existing, count)
else:
self._pattern_counts[h] = (pattern, 1)
return # first sighting — wait for more evidence
...
if count >= self._min_evidence:
del self._pattern_counts[h] # only removal path
self._saved_hashes.add(h)
if len(self._saved_hashes) > self._dedup_window: # sibling IS trimmed
self._saved_hashes.pop()
```
A pattern seen **once but never corroborated** — the common case for
one-off traffic (a unique error string, an ad-hoc shell command, a
distinct file path) — never reaches `min_evidence`, so it is **never
removed**. Over a long-lived proxy processing varied traffic,
`_pattern_counts` grows without bound and RSS climbs. The sibling
`_saved_hashes` is explicitly trimmed to `dedup_window` ("prevent
unbounded growth"); `_pattern_counts` was missed.
Reproduced directly: feeding 500 distinct one-off patterns leaves 500
entries in `_pattern_counts` (one per pattern, forever).
## Fix
Make `_pattern_counts` an LRU-ordered `OrderedDict` capped at a new
`max_pending_patterns` (default 2048):
- On each corroboration, `move_to_end(h)` so an actively-accumulating
pattern stays "fresh" and is never evicted before it can be promoted.
- On a first sighting when the accumulator is full, evict the
least-recently-corroborated pending entry (`popitem(last=False)`).
Evicting a stale one-off is safe: if it recurs it simply restarts
accumulation (delayed promotion at worst) — the same tradeoff
`_saved_hashes` already makes. Promotion at `min_evidence` is unchanged,
and the cap (2048) is generous enough that any pattern receiving repeat
sightings within a normal window reaches `min_evidence=5` long before
eviction.
## Type of Change
- [x] Bug fix (non-breaking change that fixes an issue)
- [ ] New feature
- [ ] Breaking change
- [ ] Documentation update
- [ ] Performance improvement
- [ ] Code refactoring
## Changes Made
- `headroom/memory/traffic_learner.py`: `_pattern_counts` becomes a
capped LRU `OrderedDict`; add `max_pending_patterns` (default 2048);
`move_to_end` on corroboration and evict-oldest on overflow.
- `tests/test_memory/test_traffic_learner.py`: a regression that 500
one-off patterns keep the accumulator at its cap, and one that a
corroborated pattern still promotes into `_saved_hashes` (both sync via
`asyncio.run` so they run without the pytest-asyncio plugin).
## Testing
- [x] Unit tests pass (`pytest`)
- [x] Linting passes (`ruff check .`)
- [x] Type checking passes (`mypy headroom`)
- [x] New tests added for new functionality
- [ ] Manual testing performed
### Test Output
```text
$ python -m pytest tests/test_memory/test_traffic_learner.py -q
35 failed, 109 passed
# the 35 failures are pre-existing @pytest.mark.asyncio tests that need
# pytest-asyncio (not configured in this environment); they fail identically
# on clean main (35 failed, 107 passed) and pass in CI. My two new tests are
# synchronous and pass; they add +2 passing with no new failures.
# with the fix reverted, test_pending_accumulator_is_bounded fails
# (the accumulator holds all 500 one-off patterns)
$ uvx ruff@0.15.17 check headroom/memory/traffic_learner.py tests/test_memory/test_traffic_learner.py
All checks passed!
$ uvx mypy@1.20.2 --ignore-missing-imports headroom/memory/traffic_learner.py
Success: no issues found in 1 source file
```
## Real Behavior Proof
- Environment: Windows 11, Python 3.12, project venv (`uv sync --extra
proxy`), `uvx ruff@0.15.17` / `uvx mypy@1.20.2`, pytest in the venv.
- Exact command / steps: built a `TrafficLearner(backend=None,
min_evidence=5, max_pending_patterns=8)` and drove `_accumulate` with
500 distinct one-off `ExtractedPattern`s; separately corroborated one
pattern to `min_evidence`; then reverted the source and re-ran.
- Observed result: with the fix `len(_pattern_counts)` stays at the cap
(8) after 500 one-offs, the corroborated pattern is removed from pending
and present in `_saved_hashes`, and an actively-bumped pattern survives
LRU eviction; with the fix reverted the accumulator holds all 500
one-off entries (the unbounded leak). Ran against the actual module.
- Not tested: a live multi-day proxy run measuring RSS (the leak is
inferred from the removed unbounded-growth path; the accumulator bound
is verified directly).
## Review Readiness
- [x] I have performed a self-review
- [x] This PR is ready for human review
## Checklist
- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] I have updated the CHANGELOG.md if applicable
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|---|---|---|
| .. | ||
| __init__.py | ||
| conftest.py | ||
| test_budget.py | ||
| test_core_operations.py | ||
| test_easy.py | ||
| test_embedder_mps_serialization.py | ||
| test_embedder_thread_cap.py | ||
| test_extraction.py | ||
| test_factory.py | ||
| test_factory_embedder_cache.py | ||
| test_factory_external.py | ||
| test_hierarchical.py | ||
| test_hnsw_batch_capacity.py | ||
| test_learn_flag.py | ||
| test_local_backend_search.py | ||
| test_mcp_server.py | ||
| test_qdrant_env.py | ||
| test_query_conditions.py | ||
| test_skip_helpers.py | ||
| test_supersession_repair.py | ||
| test_traffic_learner.py | ||
| test_writers.py | ||