aod-debugging-playbook

name

aod-debugging-playbook

description

Use when triaging a live Area Occupancy Detection symptom report — occupancy stuck on/won't clear, occupancy won't turn on, probability pinned at 0.99 or 0.01, wrong or spammy repair issues, a config setting that seems to be "ignored" (especially decay half-life or min_prior_override), the database growing/slow, config-flow errors, or entities showing 100% occupied right after a restart. Also load this before touching timezone/DST datetime handling, decay half-life resolution, or prior/global_prior calculation code — these are the project's three most expensive historical bug classes and this skill has the exact traps.

AOD debugging playbook

What this covers

A symptom-to-fix runbook for Area Occupancy Detection's real, recurring failure modes — the ones that have burned real debugging time across this project's history. Each symptom below gives first-checks, a discriminating experiment (an exact query/log/diagnostics field to look at, not a guess), and the fix pattern. Three specific bug classes get their own "burned lesson" trap boxes with the full incident story because they recurred multiple times: timezone/DST handling, decay half-life config normalization, and global-prior inflation.

When NOT to use this

• You need the why behind a historical incident in more narrative depth (full commit-by-commit archaeology, dead branches, abandoned drafts) → aod-failure-archaeology.
• You're deciding whether a proposed code change is safe to ship / needs a migration / could break configs → aod-change-control.
• You need the Bayesian formula itself (sigmoid/logit pipeline, exact constants, clamping) rather than "why is my number wrong" → bayesian-occupancy-reference.
• You need the full config-surface reference (every CONF_* key, defaults, what's user-facing vs internal) rather than "this one setting looks ignored" → aod-config-and-flags.
• You're improving prior/likelihood accuracy as a project, not debugging one report → aod-learning-accuracy-campaign.
• You need diagnostics/tooling mechanics (how the simulator works, visualize_distributions.py internals, diagnostics JSON schema in full) beyond what's quoted here → aod-diagnostics-and-tooling.

Debug logging recipe

Add to configuration.yaml, then restart Home Assistant:

logger:
  logs:
    custom_components.area_occupancy: debug

Logs land in Settings → System → Logs and, in the devcontainer, config/home-assistant.log. This is step 3 of the project's own debugging order — do this last, not first (see next section).

Verified: docs/docs/technical/debug.md lines 11-20; config/configuration.yaml already ships this block for the dev sensor rig.

Order of operations: diagnostics → repairs → logs

This is the project's own documented convention, not something inferred — follow it in this order:

1. Download diagnostics first. Integration card (Settings → Devices & Services → Area Occupancy Detection) → ⋮ menu → Download diagnostics. No config change needed; captures every prior/weight/evidence/decay/correlation/health value in one JSON file.
2. Check Settings → System → Repairs for sensor_health_* / pipeline_health_* issues. A stuck/unavailable sensor or stale cache is a common root cause and is surfaced automatically.
3. Only then enable debug logging and reproduce live.

Verified: docs/docs/technical/debug.md lines 1-9.

Reading the diagnostics export

Top-level shape: {"integration": {...}, "areas": [...], "database": {...}}. Each areas[] entry has current (live snapshot: probability, occupied, decay_factor, active_entity_count, decaying_entity_count, optional adjacency), prior (includes global_prior, min_prior_floor_applied), config (weights, decay, wasp/sleep settings), entities[] (per-sensor weight, prob_given_true/false, evidence, previous_evidence, last_updated, analysis_error, correlation_strength), and health. Every subsection is wrapped in try/except so one failure surfaces as a sibling <section>_error key instead of nuking the whole export.

Cheat-sheet (from the project's own diagnostics doc):

Question	Look at
Why is the area stuck occupied?	current.probability, current.decay_factor, any entities[] with unexpected evidence: true, a high correlation_strength paired with a frozen last_updated, prior.min_prior_floor_applied (non-none = a purpose/override floor is holding the value up)
Has learning finished?	prior.global_prior (null until learned); compare database.prior_count to area_count × 168
Why is correlation broken for sensor X?	entities[].analysis_error
Is health monitoring stale?	health.last_check
Is the occupied-intervals cache stale?	database.occupied_intervals_cache.<area>.valid

Verified: custom_components/area_occupancy/diagnostics.py (_area_snapshot, _collect_db_stats, async_get_config_entry_diagnostics); docs/docs/technical/diagnostics.md lines 1-116.

You can also query the SQLite DB directly (config/.storage/area_occupancy.db — a normal SQLite3 file) or run python scripts/visualize_distributions.py "<Area>" <entity_id> to plot a sensor's learned occupied-vs-unoccupied distribution against its raw data. See aod-diagnostics-and-tooling for the full toolset.

---

Symptom → triage table

1. Occupancy stuck on / won't clear

First checks	Discriminating experiment
Is decay.enabled true for this area?	Diagnostics areas[].config.decay.enabled
What half-life is actually in effect? Is decay_half_life the 0 sentinel ("use purpose default")?	Diagnostics entities[].decay vs the area's purpose default (see Purpose table below) — if stored value is 0, the effective half-life is get_default_decay_half_life(purpose), not literally instant
Is this a Wasp-in-Box or Sleep-presence entity? Both bypass purpose/sleep semantics and have their own fixed half-life	Wasp entities: half_life = 0.1s (should clear in well under a second — if one looks stuck, the wasp door/motion wiring is wrong, not decay). Sleep-presence virtual entities: SLEEP_PRESENCE_HALF_LIFE = 7200s (2h) is intentional persistent presence, not a bug
Bedroom (SLEEPING purpose) outside the configured sleep window: is a custom half-life being silently replaced by the purpose's awake_half_life (620s)?	See burned lesson #2 below (issue #481, fixed by PR #493, merged 2026-07-06) — compare the diagnostics config.decay stored half-life against Purpose.awake_half_life; if they still differ and the room still takes ~620s (10 min) to clear, the fix has regressed
Is a purpose/override prior floor holding probability near/above threshold?	Diagnostics prior.min_prior_floor_applied (none/purpose/override) — note the floor is capped at threshold - 0.01 so it alone can never push probability above threshold, but it can make an area look "always borderline occupied"
Is an adjacent area's silence extending this area's decay? (adjacent-areas feature, merged 2026-07-06 via #454)	Diagnostics current.adjacency.decay_modifier — capped at 1.75× base half-life. Still unvalidated on real homes — treat unexpected values as a candidate-feature edge case, not necessarily user error

Fix pattern: identify which of the above five mechanisms (decay disabled, sentinel resolution, wasp/sleep bypass, purpose-vs-custom half-life bug, prior floor) is actually in play before touching code — they produce visually identical "won't clear" symptoms but have completely different fixes.

Verified: custom_components/area_occupancy/data/decay.py (half-life resolution, decay_factor floors to 0.0 below a 5% threshold); data/entity.py lines ~763-774 and ~859-870 (wasp/sleep half-life overrides, SLEEP_PRESENCE_HALF_LIFE import); data/prior.py (floor capped at threshold - PRIOR_FLOOR_THRESHOLD_MARGIN, const.py:180 PRIOR_FLOOR_THRESHOLD_MARGIN = 0.01).

2. Occupancy won't turn on

First checks	Discriminating experiment
Is the sensor's evidence actually True? Evidence semantics are not "on = active" for every type	Diagnostics entities[].evidence — note InputType.DOOR's default active_states = [STATE_CLOSED]: a closed door is the active/evidence-supporting state (wasp-in-box semantics — someone closed the door behind them). This is the single easiest thing to misread as backwards
Is entity.state unavailable/unknown?	evidence returns None (not False) for unavailable/unknown/empty states — check the raw HA entity state, not just AOD's evidence field
Is effective_weight (= weight × information_gain) much lower than the configured weight?	Diagnostics entities[].analysis_error — if it's anything other than NOT_ANALYZED/MOTION_EXCLUDED, information_gain is force-clamped to 0.1 regardless of the sensor's real likelihoods, silently muting a "failed" correlation
Is the area threshold set unexpectedly high?	Diagnostics areas[].threshold (UI shows 0-100%, internal comparison is against /100; default is 50.0)
Strength multiplier: motion/sleep evidence pushes ~1.5× harder per unit of likelihood than other types, and this is not configurable via the options flow	data/entity_type.py DEFAULT_TYPES[...]["strength_multiplier"] (3.0 for MOTION/SLEEP, 2.0 for everything else) — if a non-motion sensor "feels weak" compared to motion, this is why, and it's by design

Fix pattern: reproduce with diagnostics, not logs — the evidence/analysis_error/effective_weight chain explains almost every "sensor is on but occupancy isn't" report without needing debug logging.

Verified: custom_components/area_occupancy/data/entity.py lines ~335-360 (evidence property), ~309-332 (information_gain/effective_weight); data/entity_type.py (DOOR active_states=[STATE_CLOSED], strength_multiplier table); const.py DEFAULT_THRESHOLD = 50.0.

3. Probability pinned at 0.99 or 0.01

First checks	Discriminating experiment
Both are hard clamps, not calculation artifacts: MIN_PROBABILITY=0.01, MAX_PROBABILITY=0.99 (same bounds for MIN_PRIOR/MAX_PRIOR)	const.py lines 170-173 — these are floors/ceilings applied by clamp_probability(), so "pinned at 0.99" always means something upstream pushed the logit very high, not that 0.99 is a calculated value in its own right
Is 0.01 actually a safe-fallback value rather than a learned prior?	data/analysis.py sets global_prior = 0.01 explicitly on invalid interval bounds or clock-skew guards, logging "fallback due to invalid interval bounds" / "fallback due to clock skew" — check the log line, don't assume it was learned
Is 0.99 from global-prior denominator inflation during a long quiet stretch?	See burned lesson #3 below (issue #483, fixed by PR #491, merged 2026-07-06) — actual_period_end is now always now, so this should no longer reproduce; if global_prior still keeps climbing every hourly recalculation during quiet periods, the fix has regressed

Fix pattern: don't chase weight/threshold config first — pinned values almost always trace to the prior-calculation denominator or a fallback path, both in data/analysis.py, not to sensor configuration.

Verified: const.py lines 170-176 (MIN/MAX_PROBABILITY, MIN/MAX_PRIOR); data/analysis.py (calculate_and_update_prior, fallback set_global_prior(0.01) call sites).

4. Repair issues that are wrong (false positives / spam / won't stay dismissed)

First checks	Discriminating experiment
Is the integration-level kill switch off?	CONF_HEALTH_ENABLED (const.py:93), default True (const.py:138) — if False, area.health_monitor.clear_all_issues() runs instead of checks (added PR #472 to close issue #463's "40+ issues every morning")
Is the stuck-active threshold purpose-appropriate?	Check the effective threshold = base × purpose multiplier (e.g. motion in a bedroom: 8h × 6 = 48h). The canonical threshold/multiplier/exemption table lives in aod-diagnostics-and-tooling §2. Historical context: motion's base was 2h before PR #474, which caused the original false-positive wave (issues #465, #468)
Is it a media_player.* "unavailable" complaint?	_UNAVAILABLE_EXEMPT_PREFIXES = ("media_player.",) — TVs/speakers going unavailable when powered off is exempted entirely from the unavailable check (PR #474, closing issue #466's "TV off overnight" spam)
Did a dismissed/ignored issue "come back"?	Check _is_ignored() — it reads ir.async_get(hass).async_get_issue(...)'s dismissed_version (must be a str, not just non-None, to reject stale test mocks). If a recurring condition (e.g. nightly TV-off) keeps recreating a "new" issue despite Ignore, this is PR #473's fix area (issue #463) — verify the fix is actually present: resolved issues are now partitioned into truly-resolved (deleted) vs user-ignored (left alone) so deleting doesn't wipe the ignore flag
Is InputType.SLEEP showing up in health checks at all?	It shouldn't — _EXCLUDED_TYPES = {InputType.SLEEP} excludes it globally

Repair issue ID format (useful for grepping core.issue_registry): sensor-scope = sensor_health_{area_id}_{entity_id_with_dots_replaced}_{type}; pipeline-scope = pipeline_health_{area_id}_{type}. Keyed on the stable HA area_id, not area name, so renames don't orphan issues.

Fix pattern: check the toggle first (fastest), then the purpose/threshold table, then the ignore-state mechanics — in that order of likelihood.

Verified: custom_components/area_occupancy/data/health.py lines 39-116 (thresholds/multipliers/exemption), 293-323 (_is_ignored), 824-901 (_update_repair_issues partitioning) — identical on main and this working tree; const.py:93,138 (CONF_HEALTH_ENABLED/DEFAULT_HEALTH_ENABLED, verified against main); data/config.py:189-198 (IntegrationConfig.health_enabled); commits 3471e7a (#474), b9df513 (#473), 67e53ac (#472).

⚠️ Docs trap: docs/docs/features/sensor-health.md is stale as of 2026-07-06 — it still says the motion stuck-active threshold is 2 hours and doesn't mention the purpose multipliers, the media_player.* exemption, the health_enabled toggle, or the sticky-ignore fix. Trust the code (data/health.py) over that page. (Re-check before relying on this: grep -n "2 hours" docs/docs/features/sensor-health.md.)

5. Custom setting ignored / silently reset

First checks	Discriminating experiment
Is this decay_half_life? Its 0 sentinel means "use purpose default" — a stored 0 is not literally a zero-second half-life	Diagnostics config.decay shows the stored value; if it's 0, cross-reference get_default_decay_half_life(purpose) (or the Purpose table below) for the value actually in effect. See burned lesson #2 for the exact historical bug in how values get normalized to this sentinel
Is this min_prior_override? Its 0.0 sentinel means "disabled", a different semantic from decay's "auto" — don't conflate the two 0-sentinels	const.py:134 DEFAULT_MIN_PRIOR_OVERRIDE = 0.0 # 0.0 = disabled by default
Did the config-flow silently round-trip a custom value to the sentinel on save?	Check Purpose.is_purpose_half_life(value, purpose) — as of 2026-07-06 this is correctly scoped to compare only against the selected purpose's own default (fixed by #440; the legacy bug matched against any purpose's default, see burned lesson #2)
Is the value out of the accepted config-flow range?	Decay half-life config-flow validation accepts 0 (auto) or 10 ≤ value ≤ 3600; anything else raises errors[CONF_DECAY_HALF_LIFE] = "invalid_decay_half_life" — note this range cannot literally express the SLEEPING purpose's own default of 1200s except via the 0 sentinel, which is expected, not a bug

Fix pattern: for any "my custom X is being ignored" report, first determine whether X uses a magic-sentinel-plus-lookup pattern (decay half-life does; most other settings don't) before assuming a general config-flow bug — this specific pattern is the one with the incident history.

Verified: custom_components/area_occupancy/data/purpose.py (is_purpose_half_life, docstring cites #439); config_flow.py (_apply_purpose_based_decay_default, ~line 1539, validation ~lines 1966-1971); const.py:134.

6. Database growing / slow

First checks	Discriminating experiment
Which retention constant applies? Two different numbers exist and the docs site states a third (wrong) one	RETENTION_DAYS = 365 (const.py:238) is what actually hard-deletes raw interval rows (db/operations.py::prune_old_intervals). RETENTION_RAW_INTERVALS_DAYS = 28 (const.py:248) only controls when raw intervals get rolled into daily aggregates (db/aggregation.py) — it does not delete anything. docs/docs/technical/database-schema.md claims "Raw intervals: 60 days" — this is stale/wrong; trust the constants, not that doc (re-check: grep -n "60 days" docs/docs/technical/database-schema.md)
Are diagnostic sensors writing to the recorder unnecessarily?	7 sensor classes (PriorsSensor, EvidenceSensor, DecaySensor, PresenceProbabilitySensor, EnvironmentalConfidenceSensor, ActivityConfidenceSensor, SensorHealthSensor) are disabled-by-default for newly registered areas only (PR #488, merged 2026-07-06) — existing installs' enabled/disabled state is preserved across upgrades (HA's async_get_or_create on an existing registry entry can't touch disabled_by). A full delete+re-add of an area does count as fresh registration and comes back with diagnostics disabled
Is state precision inflating row count?	CONF_SENSOR_PRECISION (default DEFAULT_SENSOR_PRECISION = ROUNDING_PRECISION = 2 decimal places) — lowering to 0 (whole-percent) measurably cuts recorder rows (PR #486, merged 2026-07-06, measured 55-79% fewer rows in the reporting install)
Is correlation analysis running on too little data / too often?	MIN_CORRELATION_SAMPLES = 50 (const.py:286) gates whether a correlation is computed at all, and confidence is discounted below full strength until well above 50 samples

Fix pattern: issue #467 ("throttle/gate DB writes") is the umbrella tracking issue and remains open as of 2026-07-06 pending real-world numbers from #486/#488 — don't assume it's fully closed just because those two PRs landed.

Verified: const.py:238,248,286,231-233 (all against main); db/operations.py (prune_old_intervals uses RETENTION_DAYS); db/aggregation.py (uses RETENTION_RAW_INTERVALS_DAYS); custom_components/area_occupancy/sensor.py (7 set_enabled_default(False) call sites, identical on main and this working tree); gh pr view 486/gh pr view 488 (both MERGED, mergedAt: 2026-07-06).

7. Config flow errors

First checks	Discriminating experiment
Which errors[key] fired?	Grep config_flow.py for the literal string, e.g. invalid_decay_half_life, invalid_threshold, invalid_weight, purpose_required, area_already_configured, area_not_found, person_already_configured, motion_required, prob_true_must_exceed_false, door_state_required/window_state_required/cover_state_required/appliance_states_required/media_states_required
Does the error key have a translation in both strings.json and translations/en.json?	These two files can drift — as of 2026-07-06, translations/en.json has a person_already_configured string that strings.json is missing entirely (re-check: grep -n person_already_configured custom_components/area_occupancy/strings.json custom_components/area_occupancy/translations/en.json). If you add a new config-flow error key, add it to both files or users see the raw key instead of a message, and hassfest (in validate.yml) may flag the mismatch
Is the failing field a numeric range check?	Weight fields use WEIGHT_MIN/WEIGHT_MAX; decay half-life uses the 0-or-[10,3600] rule from Symptom 5 above

Fix pattern: reproduce the exact flow step, read the errors["base"] or errors[<field>] key from the failed FlowResult, then grep that literal string in config_flow.py to find the guard clause — the error keys are stable strings, not translated at the Python layer.

Verified: grep -n 'errors\[.*\] = "' custom_components/area_occupancy/config_flow.py (full list of ~20 distinct error keys); translations/en.json vs strings.json diff for person_already_configured.

8. Entities unavailable / occupancy wrong immediately after restart

First checks	Discriminating experiment
Was _reconcile_entity_state() actually called during coordinator.setup()?	It should run once right after db.load_data() and correlation refresh, before the first analysis cycle — verify with grep -n "_reconcile_entity_state" coordinator.py
Are rooms showing near-100% occupied right after an upgrade/reload with no one home?	This is exactly issue #379's symptom, fixed by PR #386. Root cause: decay/evidence state is persisted to the DB on shutdown and restored verbatim on reload; if a sensor was active before shutdown, previous_evidence=True gets restored without comparing against the sensor's current (now possibly inactive) HA state, and combined with a high learned prior this drives probability toward 100%
Does the fix still hold for a regression you're investigating?	_reconcile_entity_state() does two things: (1) ticks every area's decay immediately (resolves anything that expired while unloaded) (2) calls entity.has_new_evidence() on every entity to reconcile stale previous_evidence against live HA state, which also correctly starts/stops decay based on reality

Fix pattern: if you see this symptom recur, first confirm _reconcile_entity_state() still runs unconditionally early in setup() (not gated behind a flag that could skip it) — this was a fast-startup-mode-vs-correctness tradeoff once before.

Verified: custom_components/area_occupancy/coordinator.py lines 368-383 (_reconcile_entity_state docstring and body) and its call sites at lines ~433 and ~985; gh issue view 386 (merged, closes #379).

---

Burned lesson #1: timezone / DST bugs

The rule (current, correct, and load-bearing):

Runtime arithmetic/comparisons:  timezone-aware UTC
Database persistence (SQLite):   naive UTC (tzinfo=None, interpreted as UTC)
Wall-clock bucketing (time priors, daily/weekly grouping): Home Assistant local timezone

This is a doc comment at the top of time_utils.py, and it exists because getting this wrong cost real time twice:

1. Naive-vs-aware TypeError (issues #444/#445, April 2026): dt_util.utcnow() returns tz-aware; entity.last_updated restored from storage could be tz-naive. Subtracting them raised TypeError: can't subtract offset-naive and offset-aware datetimes inside _check_stuck_sensor/_check_unavailable, causing ~87 health-check failures over ~21 hours on affected installs. Fixed by PR #446 (dt_util.as_utc(entity.last_updated) before the subtraction).
2. DST-unsafe time-of-day bucketing: the original time-prior calculation risked either double-counting or skipping the repeated/skipped local hour around a DST transition if it bucketed by naive local time directly. Fixed across two PRs: #304 (Dec 2025, introduced time_utils.py's to_utc/to_local split and bumped CONF_VERSION to 16) and #322 (Dec 2025, further UTC-storage refactor, explicitly called out DST handling improvements in its release notes).

How the current code avoids repeat-hour ambiguity: PriorAnalyzer.calculate_time_priors() walks the analysis period hour-by-hour in UTC (not local), converting each UTC instant to local only to derive the bucket key, and threads the local datetime's fold attribute through .replace(...) when constructing slot boundaries — this is what disambiguates the repeated local hour during a fall-back transition.

Wrong path people take: introducing datetime.now() or comparing a persisted (possibly naive) datetime directly against dt_util.utcnow() without going through to_utc()/from_db_utc() first. Symptom is either a crash (naive-vs-aware TypeError) or a silent one-hour bucketing error that only shows up twice a year.

Discriminating experiment: grep -n "datetime.now()" custom_components/area_occupancy/**/*.py (should be empty — everything should go through dt_util.utcnow()); for any new datetime handling, run it through time_utils.assert_utc_aware() in a test to catch a naive value immediately rather than downstream.

Fix pattern: never introduce a new datetime read/write path without deciding, explicitly, which of the three policy tiers it belongs to (arithmetic / persistence / bucketing) and routing it through the matching time_utils.py helper (to_utc, to_db_utc, from_db_utc, to_local).

Verified: custom_components/area_occupancy/time_utils.py lines 1-8 (policy docstring), 44-73 (to_local, assert_utc_aware); data/analysis.py lines ~709-721 (hour-by-hour UTC walk, fold handling, inline comment "Iterate in UTC to avoid ambiguity during DST fall-back"); commit 4dc22cf (#446); PR #304 (merged 2025-12-12, bumped CONF_VERSION to 16); PR #322 (merged 2025-12-29, "Refactor timezone handling with UTC storage", CodeRabbit summary cites "Better daylight saving time (DST) and timezone handling").

Burned lesson #2: decay half-life config bugs (three incidents, same mechanism)

The recurring failure shape: "is this half-life value the purpose default, or did the user customize it?" gets re-derived from the raw number in more than one place, and every place that does it independently is a fresh chance to get it wrong.

1. Issue #439 (2026-04-17): Purpose.is_purpose_half_life() returned True whenever the entered value matched any purpose's built-in default (12 round values: 45, 60, 90, 180, 240, 360, 450, 480, 520, 600, 620, 1200 seconds) — used by the config flow to decide whether to normalize a value to the 0 ("auto") sentinel on save. So a Living Room user who typed 600 (Office's default, not Living Room's) got silently normalized to 0, and their custom value reverted to the Living Room default (520s) on next load. Fixed same day by PR #440: the comparison is now scoped to compare only against the currently selected purpose's own default.
2. Issue #481 (2026-05-20, SETTLED — fixed by PR #493, merged 2026-07-06): the identical bug class recurred in a different code path. Decay.half_life implements a sleep/awake split for SLEEPING-purpose areas: use the configured half-life during the sleep window, switch to the purpose's awake_half_life (620s) outside it. The switch applied unconditionally — so a user's custom 10-second half-life got silently replaced by 620s (a ~15 minute clear-out) during every waking hour, with no way to keep a short custom half-life active outside the sleep window. Reported symptom: bedroom that should clear in ~10s instead took ~15 minutes.
3. PR #493 (merged 2026-07-06): fix mirrors #440's pattern exactly — the awake/sleep switch is restricted to only engage when the area's half-life still equals the purpose's own default (i.e., the user left it on auto). A custom value now wins at all times of day. Implemented as Decay._resolve_purpose_half_life()'s if self._base_half_life != self._purpose.half_life: return self._base_half_life guard, with the adjacent-areas modifier_factor (from #454, also merged 2026-07-06) multiplying on top of the resolved value in the half_life property.

Wrong path people take: fixing the config-flow-side normalization (#440) and assuming the bug class is closed. It reappeared in the runtime decay-resolution code (data/decay.py), a completely separate file, over a month later — because both places independently ask "is this a default or a custom value?" by comparing against known defaults, rather than carrying an explicit "this was customized" flag through the pipeline.

Discriminating experiment: for a SLEEPING-purpose area, set a custom half-life that is not 1200s (the purpose default) or 620s (awake_half_life), then check the diagnostics config.decay value both inside and outside the configured sleep window — it should read the same custom value in both cases (confirm this now holds post-#493). Also check any other purpose combined with a numerically coincidental custom value (e.g. Living Room + 600s, Office's default) to catch a #439-style regression.

Fix pattern: any code that decides "is this the default or a custom override" for a purpose-scoped setting must scope the comparison to the specific selected purpose only — never match against the full list of all purposes' defaults. If you add a new purpose-scoped setting with a similar auto/custom split, write a test for exactly this coincidental-value case before shipping.

Verified: custom_components/area_occupancy/data/purpose.py (is_purpose_half_life docstring explicitly cites #439 and describes the legacy bug); custom_components/area_occupancy/data/decay.py lines ~81-122 (_resolve_purpose_half_life, the != self._purpose.half_life guard now gates the awake/sleep switch — confirmed present and fixed on main as of 2026-07-06, HEAD 17b71d2); config_flow.py ~line 1539 (Purpose.is_purpose_half_life(user_set_decay, purpose), comment citing #439); gh pr view 440, gh pr view 493 (both state MERGED, #493 mergedAt 2026-07-06, body: "mirrors the custom-vs-default semantics established for #440").

Burned lesson #3: prior pinned at 0.99 (#483 quiet-tail denominator) — SETTLED, fixed by PR #491, merged 2026-07-06

Root cause: PriorAnalyzer.calculate_and_update_prior() computes global_prior = occupied_duration / actual_period_duration. The code used to set actual_period_end = last_interval_end (instead of now) whenever the area had been quiet for more than 3600 seconds (1 hour) before the analysis run. This truncated the denominator's "known unoccupied" tail while the numerator kept counting all historically occupied seconds — every hourly analysis cycle that ran during an overnight or weekend quiet stretch pushed global_prior a little higher, and repeated cycles compounded the effect until it saturated at the MAX_PRIOR = 0.99 clamp.

Manifestation (from the reporter, @mscharwere): a kitchen mmWave sensor with a true occupancy rate of ~28-35% had its learned global_prior pinned at 0.99 — nowhere near the actual rate.

Wrong path people take: treating a 0.99-pinned prior as a sensor/weight/threshold misconfiguration and tuning those instead. The actual defect was in the learning code's period-window math, not in anything sensor-facing — nothing in the entity config was wrong.

Discriminating experiment: check whether the area has had any extended quiet stretch (no occupied intervals for >1h) before recent analysis cycles, and whether global_prior has been monotonically climbing cycle over cycle rather than settling. Diagnostics' prior.global_prior field plus manual arithmetic (occupied_duration_seconds / total_period_seconds over the full, non-truncated window) will disagree with the stored value if this bug is still active anywhere — but on current main it should no longer reproduce at all.

Status as of 2026-07-06: fixed on main (HEAD 17b71d2). data/analysis.py now sets actual_period_end = now unconditionally — the old if (now - last_interval_end).total_seconds() > 3600: actual_period_end = last_interval_end truncation branch is gone. PR #491 merged 2026-07-06; the original branch's stated purpose (guarding a degenerate just-after-startup period) is covered instead by a separate actual_period_duration <= 0 guard.

Lineage: this is not the first time prior calculation has been reworked — PRs #246 ("Refactor time-prior calculation to use Python instead of SQL"), #251 ("Simplify prior calculation to motion/presence sensors only"), #266 ("Restructure prior calculation flow with immediate database persistence"), and #356 ("Improve prior calculation accuracy") all touched this same area before #483/#491. Treat data/analysis.py's prior-calculation code as chronically fragile — favor small, well-tested changes with an explicit before/after numeric example in the PR description over broad refactors, even now that this particular incident is closed.

Fix pattern: any time you touch the observation-period bounds in prior calculation, write a test with a concrete numeric scenario (known occupied seconds, known total seconds, expected prior) — the bug here was caught by exactly the kind of test (test_valid_calculation_sets_correct_prior) that had previously encoded the buggy expected value (asserting 0.99 where 0.25 was correct) and had to be corrected alongside the fix.

Verified: custom_components/area_occupancy/data/analysis.py lines ~516-518 (actual_period_end = now, unconditional, truncation branch removed); gh issue view 483 (closed); gh pr view 491 (state MERGED, mergedAt 2026-07-06, body confirms root cause and fix); gh pr view 246, gh pr view 251, gh pr view 266, gh pr view 356 (all MERGED, all prior-calculation titles).

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Provenance and maintenance

Date-stamped 2026-07-06 (post-merge sweep), integration version still 2026.5.17 — none of the 2026-07-06 merge wave (#454, #486, #488, #491-496, etc.) has shipped in a tagged release yet (git log -1 --oneline on main → 17b71d2 feat: adjacent-areas — learned next-door room influence (#454)). All line numbers and constant values in this file were read directly from main via git show main:<path>; the working tree is now checked out to main itself (the former feat/adjacent-areas branch merged and is gone), so working-tree and main facts are identical as of this sweep.

Re-verification commands by volatile fact category:

• Clamp/threshold constants (MIN/MAX_PROBABILITY, MIN/MAX_PRIOR, TIME_PRIOR_*_BOUND, PRIOR_FLOOR_THRESHOLD_MARGIN, RETENTION_DAYS, RETENTION_RAW_INTERVALS_DAYS, MIN_CORRELATION_SAMPLES, DEFAULT_THRESHOLD, DEFAULT_HEALTH_ENABLED, DEFAULT_MIN_PRIOR_OVERRIDE): git show main:custom_components/area_occupancy/const.py | grep -n "MIN_PROBABILITY\|MAX_PROBABILITY\|MIN_PRIOR\|MAX_PRIOR\|RETENTION\|MIN_CORRELATION_SAMPLES\|DEFAULT_THRESHOLD\|HEALTH_ENABLED\|MIN_PRIOR_OVERRIDE"
• Purpose half-life table: git show main:custom_components/area_occupancy/data/purpose.py | grep -n "_half_life="
• Decay half-life sentinel resolution and sleep/awake switch: git show main:custom_components/area_occupancy/data/decay.py and git show main:custom_components/area_occupancy/data/entity.py | grep -n "half_life"
• Health-check thresholds/exemptions/toggle: git show main:custom_components/area_occupancy/data/health.py | sed -n '39,120p'
• Config-flow error keys and half-life validation range: git show main:custom_components/area_occupancy/config_flow.py | grep -n 'errors\[.*\] = "' and grep -n "10 or decay_window > 3600" custom_components/area_occupancy/config_flow.py
• strings.json / translations drift: diff <(grep -o '"[a-z_]*":' custom_components/area_occupancy/strings.json) <(grep -o '"[a-z_]*":' custom_components/area_occupancy/translations/en.json)
• Diagnostic-sensor default-disabled list: grep -n "set_enabled_default(False)" custom_components/area_occupancy/sensor.py
• DB retention docs staleness: grep -n "60 days" docs/docs/technical/database-schema.md
• Restart reconciliation: grep -n "_reconcile_entity_state" custom_components/area_occupancy/coordinator.py
• Open/merged status of every cited PR/issue (#440, #481, #483, #486, #488, #491, #493, #454, #386/#379, #439, #444, #445, #446, #463, #465, #466, #467, #468, #472, #473, #474): gh pr view <n> --json state,mergedAt,baseRefName / gh issue view <n> --json state — as of this sweep (2026-07-06) #440, #481/#493, #483/#491, #454, #486, #488 are all MERGED/closed; #466 and #467 remain OPEN — re-check before describing anything as shipped in a release (the integration version itself hasn't bumped past 2026.5.17 yet).
• Integration version / commit: git log -1 --oneline (on main; the working tree now tracks main directly post-merge — check git branch --show-current first if this changes again).