diff --git a/pyproject.toml b/pyproject.toml
index 1ae32e14..0c75ed59 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -106,6 +106,7 @@ per-file-ignores = {"src/brainlayer/cli/__init__.py" = ["F401"]}
 
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
+pythonpath = ["src"]
 markers = [
     "integration: tests that need the real production DB (268K+ chunks)",
     "slow: tests that load ML models or take >30s",
diff --git a/src/brainlayer/pipeline/enrichment_tiers.py b/src/brainlayer/pipeline/enrichment_tiers.py
new file mode 100644
index 00000000..54bdf27f
--- /dev/null
+++ b/src/brainlayer/pipeline/enrichment_tiers.py
@@ -0,0 +1,138 @@
+"""Tiered enrichment selectivity for BrainLayer.
+
+Assigns each chunk a processing tier based on source, content type, and age:
+
+  T0 (IMMEDIATE): manual/digest — always enrich, highest priority
+  T1 (HOURLY):    recent claude_code chunks — hourly local enrichment
+  T2 (LAZY):      old claude_code backlog — lazy remote batch
+  T3 (EXPLICIT):  youtube transcripts — only when explicitly triggered
+
+Design note: tiers are IntEnum so T0 < T1 < T2 < T3 comparisons work naturally
+and callers can filter "up to tier N" with `tier <= max_tier`.
+"""
+
+from datetime import datetime, timedelta, timezone
+from enum import IntEnum
+from typing import List, Optional, Set
+
+# ── Tier definition ──────────────────────────────────────────────────────
+
+
+class EnrichmentTier(IntEnum):
+    T0_IMMEDIATE = 0  # manual / digest — enrich immediately
+    T1_HOURLY = 1  # recent claude_code — hourly local run
+    T2_LAZY = 2  # old claude_code backlog — lazy / remote batch
+    T3_EXPLICIT = 3  # youtube — explicit request only
+
+
+# ── Constants ────────────────────────────────────────────────────────────
+
+# Sources that are always T0 regardless of age or content type.
+T0_SOURCES: frozenset = frozenset({"manual", "digest"})
+
+# Sources that are always T3 regardless of age or content type.
+T3_SOURCES: frozenset = frozenset({"youtube"})
+
+# Default recency window: chunks within this many days are T1, older are T2.
+DEFAULT_RECENCY_DAYS: int = 7
+
+# High-value content types enriched at T1 (and T2 for old backlog).
+T1_CONTENT_TYPES: List[str] = ["ai_code", "stack_trace", "user_message", "assistant_text"]
+
+# Content types that should never be enriched (low-signal noise).
+SKIP_CONTENT_TYPES: frozenset = frozenset({"noise"})
+
+# Only these sources participate in the T1/T2 recency gate.
+# Unrecognised sources fall through to T2 (lazy backlog) rather than T1.
+T1_T2_SOURCES: frozenset = frozenset({"claude_code"})
+
+
+# ── Classifier ───────────────────────────────────────────────────────────
+
+
+def classify_chunk_tier(
+    source: str,
+    content_type: str,
+    created_at: Optional[str],
+    recency_days: int = DEFAULT_RECENCY_DAYS,
+) -> EnrichmentTier:
+    """Return the enrichment tier for a chunk.
+
+    Args:
+        source:        The chunk source field (e.g. "claude_code", "youtube", "manual").
+        content_type:  The chunk content_type field (e.g. "ai_code", "assistant_text").
+        created_at:    ISO timestamp string when the chunk was created, or None.
+        recency_days:  Window (days) for T1 vs T2 split (default 7).
+
+    Returns:
+        EnrichmentTier for the chunk.
+    """
+    # Noise is never worth enriching, regardless of source.
+    if content_type in SKIP_CONTENT_TYPES:
+        return EnrichmentTier.T3_EXPLICIT
+
+    # T0: always-on sources (manual brain_store, digested documents)
+    if source in T0_SOURCES:
+        return EnrichmentTier.T0_IMMEDIATE
+
+    # T3: archival sources never touched by the default pipeline
+    if source in T3_SOURCES:
+        return EnrichmentTier.T3_EXPLICIT
+
+    # Only recognised T1/T2 sources participate in the recency gate.
+    # Unknown sources default to lazy backlog (T2) rather than crowding T1.
+    if source not in T1_T2_SOURCES:
+        return EnrichmentTier.T2_LAZY
+
+    # Claude code: age determines tier.
+    if _is_recent(created_at, recency_days):
+        return EnrichmentTier.T1_HOURLY
+    return EnrichmentTier.T2_LAZY
+
+
+def _is_recent(created_at: Optional[str], recency_days: int) -> bool:
+    """Return True if created_at falls within the recency window."""
+    if created_at is None:
+        return False
+    try:
+        dt = datetime.fromisoformat(created_at)
+        if dt.tzinfo is None:
+            dt = dt.replace(tzinfo=timezone.utc)
+        cutoff = datetime.now(timezone.utc) - timedelta(days=recency_days)
+        return dt >= cutoff
+    except (ValueError, TypeError):
+        return False
+
+
+# ── Selectors ────────────────────────────────────────────────────────────
+
+
+def get_tier_content_types(tier: EnrichmentTier) -> List[str]:
+    """Return the content types relevant for a given tier.
+
+    All tiers currently share the same high-value content type list.
+    This function exists so callers can parametrize queries without
+    hard-coding content types.
+    """
+    return list(T1_CONTENT_TYPES)
+
+
+def get_tier_source_filter(tier: EnrichmentTier) -> Set[str]:
+    """Return the set of *allowed* sources for a given tier.
+
+    Useful for building SQL IN clauses or filtering chunk lists.
+
+    T0 → {manual, digest}
+    T1 → {claude_code}   (explicitly excludes youtube)
+    T2 → {claude_code}   (old backlog only)
+    T3 → {youtube}
+    """
+    if tier == EnrichmentTier.T0_IMMEDIATE:
+        return set(T0_SOURCES)
+    if tier == EnrichmentTier.T1_HOURLY:
+        return {"claude_code"}
+    if tier == EnrichmentTier.T2_LAZY:
+        return {"claude_code"}
+    if tier == EnrichmentTier.T3_EXPLICIT:
+        return set(T3_SOURCES)
+    return set()  # pragma: no cover
diff --git a/tests/test_enrichment_tiers.py b/tests/test_enrichment_tiers.py
new file mode 100644
index 00000000..ca4033ac
--- /dev/null
+++ b/tests/test_enrichment_tiers.py
@@ -0,0 +1,225 @@
+"""TDD tests for tiered enrichment selectivity.
+
+Tiers:
+  T0 (IMMEDIATE): manual/digest sources and high-signal types (decision, mistake)
+  T1 (HOURLY):    recent claude_code chunks (ai_code, stack_trace, user_message, assistant_text)
+  T2 (LAZY):      old claude_code backlog (older than recency_days)
+  T3 (EXPLICIT):  youtube transcripts — only when explicitly requested
+"""
+
+from datetime import datetime, timedelta, timezone
+
+from brainlayer.pipeline.enrichment_tiers import (
+    EnrichmentTier,
+    classify_chunk_tier,
+    get_tier_content_types,
+    get_tier_source_filter,
+)
+
+# ── Helpers ─────────────────────────────────────────────────────────────
+
+
+def _dt(days_ago: int) -> str:
+    """Return ISO timestamp N days ago in UTC."""
+    return (datetime.now(timezone.utc) - timedelta(days=days_ago)).isoformat()
+
+
+RECENT = _dt(3)
+OLD = _dt(30)
+VERY_OLD = _dt(365)
+
+# ── T0: IMMEDIATE — manual / digest / high-signal memory types ───────────
+
+
+def test_manual_source_is_tier0():
+    """Manually stored chunks (brain_store) must always be tier 0."""
+    tier = classify_chunk_tier(source="manual", content_type="assistant_text", created_at=RECENT)
+    assert tier == EnrichmentTier.T0_IMMEDIATE
+
+
+def test_digest_source_is_tier0():
+    """Digested documents must always be tier 0."""
+    tier = classify_chunk_tier(source="digest", content_type="assistant_text", created_at=RECENT)
+    assert tier == EnrichmentTier.T0_IMMEDIATE
+
+
+def test_manual_source_is_tier0_regardless_of_age():
+    """Manual chunks should be T0 even if they are old."""
+    tier = classify_chunk_tier(source="manual", content_type="assistant_text", created_at=VERY_OLD)
+    assert tier == EnrichmentTier.T0_IMMEDIATE
+
+
+def test_digest_source_is_tier0_regardless_of_age():
+    """Digest chunks should be T0 even if they are old."""
+    tier = classify_chunk_tier(source="digest", content_type="ai_code", created_at=VERY_OLD)
+    assert tier == EnrichmentTier.T0_IMMEDIATE
+
+
+# ── T1: HOURLY — recent claude_code ──────────────────────────────────────
+
+
+def test_recent_claude_code_ai_code_is_tier1():
+    """Recent ai_code from claude_code sessions is tier 1."""
+    tier = classify_chunk_tier(source="claude_code", content_type="ai_code", created_at=RECENT)
+    assert tier == EnrichmentTier.T1_HOURLY
+
+
+def test_recent_claude_code_stack_trace_is_tier1():
+    """Recent stack_trace from claude_code sessions is tier 1."""
+    tier = classify_chunk_tier(source="claude_code", content_type="stack_trace", created_at=RECENT)
+    assert tier == EnrichmentTier.T1_HOURLY
+
+
+def test_recent_claude_code_user_message_is_tier1():
+    """Recent user_message from claude_code sessions is tier 1."""
+    tier = classify_chunk_tier(source="claude_code", content_type="user_message", created_at=RECENT)
+    assert tier == EnrichmentTier.T1_HOURLY
+
+
+def test_recent_claude_code_assistant_text_is_tier1():
+    """Recent assistant_text from claude_code sessions is tier 1."""
+    tier = classify_chunk_tier(source="claude_code", content_type="assistant_text", created_at=RECENT)
+    assert tier == EnrichmentTier.T1_HOURLY
+
+
+def test_today_claude_code_is_tier1():
+    """Chunks from today (0 days ago) are recent."""
+    today = _dt(0)
+    tier = classify_chunk_tier(source="claude_code", content_type="ai_code", created_at=today)
+    assert tier == EnrichmentTier.T1_HOURLY
+
+
+def test_within_recency_window_is_tier1():
+    """Chunks well within the recency window (6 days) are T1.
+
+    The boundary (7 days) is not tested at microsecond precision here because
+    classify_chunk_tier evaluates 'now' slightly after the timestamp is captured.
+    test_just_past_recency_window_is_tier2 covers the other side at 8 days.
+    """
+    at_boundary = _dt(6)
+    tier = classify_chunk_tier(source="claude_code", content_type="ai_code", created_at=at_boundary)
+    assert tier == EnrichmentTier.T1_HOURLY
+
+
+# ── T2: LAZY — old claude_code backlog ───────────────────────────────────
+
+
+def test_old_claude_code_assistant_text_is_tier2():
+    """Old assistant_text backlog (>7 days) from claude_code is tier 2."""
+    tier = classify_chunk_tier(source="claude_code", content_type="assistant_text", created_at=OLD)
+    assert tier == EnrichmentTier.T2_LAZY
+
+
+def test_old_claude_code_user_message_is_tier2():
+    """Old user_message backlog from claude_code is tier 2."""
+    tier = classify_chunk_tier(source="claude_code", content_type="user_message", created_at=OLD)
+    assert tier == EnrichmentTier.T2_LAZY
+
+
+def test_very_old_claude_code_is_tier2():
+    """Very old claude_code chunks (>1 year) are still only T2, not T3."""
+    tier = classify_chunk_tier(source="claude_code", content_type="assistant_text", created_at=VERY_OLD)
+    assert tier == EnrichmentTier.T2_LAZY
+
+
+def test_just_past_recency_window_is_tier2():
+    """Chunks just past the recency window (8 days) are T2."""
+    just_past = _dt(8)
+    tier = classify_chunk_tier(source="claude_code", content_type="assistant_text", created_at=just_past)
+    assert tier == EnrichmentTier.T2_LAZY
+
+
+# ── T3: EXPLICIT — youtube transcripts ──────────────────────────────────
+
+
+def test_youtube_source_is_tier3():
+    """YouTube transcript chunks are always tier 3 regardless of content type or age."""
+    tier = classify_chunk_tier(source="youtube", content_type="assistant_text", created_at=RECENT)
+    assert tier == EnrichmentTier.T3_EXPLICIT
+
+
+def test_youtube_source_old_is_still_tier3():
+    """Old YouTube chunks stay T3."""
+    tier = classify_chunk_tier(source="youtube", content_type="assistant_text", created_at=VERY_OLD)
+    assert tier == EnrichmentTier.T3_EXPLICIT
+
+
+def test_unknown_source_defaults_to_tier2():
+    """Unknown/unrecognized source defaults to T2 (lazy backlog), regardless of age.
+
+    Only claude_code participates in T1 (recency-gated). Unrecognised sources
+    are treated as lazy backlog to prevent them from crowding hourly enrichment.
+    """
+    tier = classify_chunk_tier(source="unknown", content_type="assistant_text", created_at=RECENT)
+    assert tier == EnrichmentTier.T2_LAZY
+
+
+def test_unknown_source_old_is_tier2():
+    """Old unknown source is also T2 (same as recent unknown)."""
+    tier = classify_chunk_tier(source="unknown", content_type="assistant_text", created_at=OLD)
+    assert tier == EnrichmentTier.T2_LAZY
+
+
+# ── Noise content type — never enrich ────────────────────────────────────
+
+
+def test_noise_content_type_is_tier3_explicit():
+    """Noise chunks should never be enriched by default (T3 = explicit only)."""
+    tier = classify_chunk_tier(source="claude_code", content_type="noise", created_at=RECENT)
+    assert tier == EnrichmentTier.T3_EXPLICIT
+
+
+def test_noise_content_type_overrides_t0_source():
+    """Even a T0 source should yield T3 if content_type is noise."""
+    tier = classify_chunk_tier(source="manual", content_type="noise", created_at=RECENT)
+    assert tier == EnrichmentTier.T3_EXPLICIT
+
+
+# ── None / missing created_at ────────────────────────────────────────────
+
+
+def test_none_created_at_defaults_to_tier2_for_claude_code():
+    """Chunks with no created_at timestamp are treated as old (T2 for claude_code)."""
+    tier = classify_chunk_tier(source="claude_code", content_type="assistant_text", created_at=None)
+    assert tier == EnrichmentTier.T2_LAZY
+
+
+# ── get_tier_content_types ───────────────────────────────────────────────
+
+
+def test_get_tier_content_types_returns_high_value_for_t1():
+    """T1 content types should include the core high-value types."""
+    types = get_tier_content_types(EnrichmentTier.T1_HOURLY)
+    assert "ai_code" in types
+    assert "stack_trace" in types
+    assert "user_message" in types
+    assert "assistant_text" in types
+
+
+# ── get_tier_source_filter ───────────────────────────────────────────────
+
+
+def test_get_tier_source_filter_t1_excludes_youtube():
+    """T1 source filter must exclude youtube so it's not processed hourly."""
+    sources = get_tier_source_filter(EnrichmentTier.T1_HOURLY)
+    assert "youtube" not in sources
+
+
+def test_get_tier_source_filter_t0_includes_manual_and_digest():
+    """T0 source filter must include manual and digest sources."""
+    sources = get_tier_source_filter(EnrichmentTier.T0_IMMEDIATE)
+    assert "manual" in sources
+    assert "digest" in sources
+
+
+def test_get_tier_source_filter_t3_only_youtube():
+    """T3 source filter should only include youtube."""
+    sources = get_tier_source_filter(EnrichmentTier.T3_EXPLICIT)
+    assert sources == {"youtube"}
+
+
+def test_tier_ordering():
+    """Lower tier numbers should be higher priority (T0 < T1 < T2 < T3)."""
+    assert EnrichmentTier.T0_IMMEDIATE < EnrichmentTier.T1_HOURLY
+    assert EnrichmentTier.T1_HOURLY < EnrichmentTier.T2_LAZY
+    assert EnrichmentTier.T2_LAZY < EnrichmentTier.T3_EXPLICIT