02 — Test b: Domain/Professional Axis Filter Plan (READ-ONLY)

Goal: Given a professional/domain axis value drawn from the Constitution's classification vocabulary, return the exact set of IU pieces carrying that axis tag — DOT-callable, config-driven, automated, evidence-producing. This is a read-only test: zero mutation.

Owner law: Điều 38/39 (IU axis). Mutation: none. Gate: none. Approval: none. Event/queue impact: none. Rollback: N/A (read-only). Readiness: HIGH.

1. Live substrate (verified)

• iu_three_axis_envelope (216 rows; 1 per IU): axis_b_tags jsonb + axis_b_tags_by_source jsonb.
• iu_metadata_tag (536 rows) keyed by tag_key; iu_metadata_tag_registry (36 rows) = the tag vocabulary.
• Views: v_iu_metadata_envelope, v_ui_iu_three_axis_envelope.
• Refresh fn: fn_iu_three_axis_envelope_refresh (+ _if_stale, _drift_check); DOT dot_iu_rebuild_metadata_axes. Gate iu_core.three_axis_auto_refresh_enabled=false → envelopes are manually refreshed; the filter reads them as-is.

2. Input dataset choices

Use the existing live corpus (216 IUs, no new data). Candidate domain-axis values (from live iu_metadata_tag.tag_key distribution):

Axis-B family	Example values (live counts)
legal_domain:*	knowledge_systems (16), governance (5), technology (4)
topic:*	knowledge_graph (10), architecture (5), governance (3), dot_trigger (3), workflow (2)
sectype:*	technical_spec (25), governance_process (18), principle (11), process (10)
doc:*	DIEU-35 (36), DIEU-28 (27), DIEU-32 (23), DIEU-39 (16)
kind:*	law_unit (187), design_doc_section (29)

Primary test value: legal_domain:knowledge_systems (expected 16 matches) — the cleanest "professional/domain axis" example. Secondary: topic:knowledge_graph (10).

3. Filter contract

filter_axis_b(
  p_tag_key            text,        -- e.g. 'legal_domain:knowledge_systems'  (required, must exist in registry)
  p_lifecycle_status   text = NULL, -- optional narrowing (e.g. 'enacted')
  p_doc_code           text = NULL, -- optional axis-A doc scope (e.g. 'DIEU-37')
  p_match_mode         text = 'exact' -- 'exact' | 'prefix' (prefix → 'legal_domain:%')
) RETURNS TABLE(unit_id uuid, canonical_address text, axis_a_doc_code text,
                axis_a_sort_order int, axis_b_tags jsonb, lifecycle_status text)

• Source of truth = iu_three_axis_envelope (read) joined to information_unit for address; tag membership validated against iu_metadata_tag / iu_metadata_tag_registry.
• No-hardcode: p_tag_key must resolve to a row in iu_metadata_tag_registry; reject unknown keys (do not silently return empty).
• Config-driven: result ordering by axis_a_doc_code, axis_a_sort_order (stable, reconstruct-compatible).

4. Expected output shape

A deterministic, ordered rowset. For legal_domain:knowledge_systems: 16 rows, each with unit_id, canonical_address, axis_a_doc_code, axis_b_tags containing the key. Output is also emitted as a JSON evidence blob for the harness.

5. Needed DOT wrapper

dot_iu_filter_axis_b (read-only, non-mutating) — see deliverable 07. It wraps filter_axis_b(...), writes a dot_iu_command_run audit row (mutating=false), and returns {count, rows, registry_validated:true}. Gap: this command does not exist in the 42-command catalog (catalog has dot_iu_rebuild_metadata_axes = a refresh, not a filter).

6. No-mutation proof

• Function is declared STABLE, contains only SELECT; no INSERT/UPDATE/DELETE.
• Harness wraps the call in BEGIN; ... ; ROLLBACK; and asserts table row-count deltas = 0 across information_unit, iu_three_axis_envelope, iu_metadata_tag, event_outbox.
• dot_iu_command_run.mutating=false recorded.

7. Assertions

1. Cardinality: count(filter) == count(direct iu_metadata_tag membership for the key). For legal_domain:knowledge_systems == 16.
2. Set equality: the unit_id set from the envelope path == the unit_id set from the raw iu_metadata_tag path (no envelope drift). If unequal → axis-B envelope is stale → surfaces fn_iu_three_axis_envelope_drift_check finding.
3. Ordering determinism: two consecutive calls return byte-identical ordered output.
4. Registry validation: unknown key (e.g. legal_domain:does_not_exist) → explicit refusal, not empty success.
5. Zero mutation: all deltas 0 (per §6).

8. Evidence rows

• dot_iu_command_run row (mutating=false, input params, count, duration).
• JSON: {tag_key, match_mode, count, unit_ids[], drift_ok, registry_validated, deltas_zero}.
• Stored under the harness run id for KB report attachment.

9. Failure modes

Mode	Detection	Handling
Envelope stale (drift)	assertion 2 set-inequality; fn_iu_three_axis_envelope_drift_check	report drift, do NOT auto-refresh inside read test (refresh is a separate gated op)
Unknown tag key	registry validation	refuse with indexed error
Empty result for valid key	count==0 but key in registry	PASS with count 0 only if raw path also 0; else FAIL (drift)
Non-deterministic order	assertion 3	add explicit ORDER BY; FAIL until fixed

10. Exact PASS criteria

PASS iff: assertions 1–5 all hold for at least 2 distinct axis-B families (one legal_domain:*, one topic:*), the DOT wrapper records mutating=false, and zero-mutation deltas confirmed. Otherwise PARTIAL (drift found, documented) or FAIL.

11. Author-ready implementation note

Implement filter_axis_b as a STABLE SQL function + dot_iu_filter_axis_b catalog entry in macro IU_TEST_B_C_READONLY_HARNESS_IMPLEMENTATION_XHIGH (deliverable 10, prompt #1). No gate, no approval. Reuse iu_three_axis_envelope + iu_metadata_tag_registry; do not create a new tag store (live-ready-means-use-not-rewrite). Pair b and c in one harness since both are read-only and share the envelope.