diff --git a/src/omni_pca/program_engine.py b/src/omni_pca/program_engine.py
index bc92ed6..b6e2f15 100644
--- a/src/omni_pca/program_engine.py
+++ b/src/omni_pca/program_engine.py
@@ -476,6 +476,135 @@ EVENT_AC_POWER_OFF: int = 772
 EVENT_AC_POWER_ON: int = 773
 
 
+# --------------------------------------------------------------------------
+# Clausal chains (Phase 5)
+# --------------------------------------------------------------------------
+
+
+@dataclass(frozen=True, slots=True)
+class ClausalChain:
+    """One multi-record clausal program.
+
+    On firmware ≥3.0.0 each clausal program occupies a contiguous run of
+    program slots: one head record (WHEN / AT / EVERY), zero or more
+    AND/OR condition records, then one or more THEN action records.
+
+    The engine groups the panel's program table into chains by walking
+    forward from each clausal head until the next head / non-clausal /
+    empty slot. The fields below carry the typed view of each role:
+
+    * ``head`` — the trigger record (WHEN: event-driven, AT: time-of-day,
+      EVERY: recurring interval)
+    * ``conditions`` — zero or more AND/OR records guarding the action
+    * ``actions`` — one or more THEN records firing when conditions pass
+    """
+
+    head: Program
+    conditions: tuple[Program, ...]
+    actions: tuple[Program, ...]
+
+
+def build_chains(
+    programs: tuple[Program, ...],
+) -> tuple[ClausalChain, ...]:
+    """Walk a slot-ordered Program tuple, gathering clausal chains.
+
+    Heads (WHEN/AT/EVERY) start a chain; subsequent AND/OR/THEN records
+    in adjacent slots join it. A chain ends when:
+      * the next slot is another head (start of next chain)
+      * the next slot is not a multi-record type (FREE, TIMED, etc.)
+      * the next slot is empty
+      * we run out of records
+
+    Returns chains in head-slot order. Chains with no THEN records are
+    dropped (they have no action to fire).
+    """
+    by_slot: dict[int, Program] = {
+        p.slot: p for p in programs if p.slot is not None and not p.is_empty()
+    }
+    if not by_slot:
+        return ()
+    heads = sorted(
+        (s for s, p in by_slot.items() if p.prog_type in (
+            int(ProgramType.WHEN),
+            int(ProgramType.AT),
+            int(ProgramType.EVERY),
+        )),
+    )
+    out: list[ClausalChain] = []
+    for head_slot in heads:
+        head = by_slot[head_slot]
+        conditions: list[Program] = []
+        actions: list[Program] = []
+        slot = head_slot + 1
+        while slot in by_slot:
+            rec = by_slot[slot]
+            ptype = rec.prog_type
+            if ptype in (
+                int(ProgramType.WHEN),
+                int(ProgramType.AT),
+                int(ProgramType.EVERY),
+            ):
+                break  # next chain's head
+            if ptype == int(ProgramType.AND) or ptype == int(ProgramType.OR):
+                conditions.append(rec)
+            elif ptype == int(ProgramType.THEN):
+                actions.append(rec)
+            else:
+                break  # ran into a non-clausal record (TIMED, REMARK, ...)
+            slot += 1
+        if actions:
+            out.append(ClausalChain(
+                head=head,
+                conditions=tuple(conditions),
+                actions=tuple(actions),
+            ))
+    return tuple(out)
+
+
+def evaluate_conditions(
+    conditions: tuple[Program, ...],
+    *,
+    is_satisfied,
+) -> bool:
+    """Evaluate an AND/OR condition list against an external predicate.
+
+    Phase 5 v1 keeps the evaluator deliberately simple: each AND/OR
+    record is reduced to a boolean by the caller-supplied
+    ``is_satisfied(condition_program)`` predicate, then combined with
+    standard short-circuit AND-of-OR-groups semantics:
+
+      * Records form left-to-right groups separated by OR boundaries
+        — each OR record *starts a new group*.
+      * Within a group, every AND record's predicate must be True
+        (logical AND).
+      * The overall result is True if *any* group's AND-result is True
+        (logical OR across groups).
+
+    An empty conditions tuple is unconditionally True — a "WHEN ...
+    THEN ..." chain with no AND/OR guard always runs its actions.
+
+    The detailed semantic decode of each AND/OR record (zone-state
+    checks, time-of-day comparisons, structured TEMP > 70-style ops)
+    is deferred to a follow-up; for now ``is_satisfied`` is the
+    integration point tests / HA code use to feed in evaluated values.
+    """
+    if not conditions:
+        return True
+    # Split into groups separated by OR records.
+    groups: list[list[Program]] = [[]]
+    for c in conditions:
+        if c.prog_type == int(ProgramType.OR):
+            groups.append([c])
+        else:
+            groups[-1].append(c)
+    # Any group whose ANDs all pass = overall pass.
+    for group in groups:
+        if all(is_satisfied(c) for c in group):
+            return True
+    return False
+
+
 # --------------------------------------------------------------------------
 # Engine
 # --------------------------------------------------------------------------
@@ -534,14 +663,39 @@ class ProgramEngine:
                 continue
         self._programs: tuple[Program, ...] = tuple(decoded)
         self._classified = classify(self._programs)
+        self._chains = build_chains(self._programs)
         self._tasks: list[asyncio.Task[None]] = []
         self._running = False
-        # event_id → list of EVENT programs that fire on it. Built lazily
-        # in start() so callers can mutate state.programs between init
-        # and start (e.g. a test seeding extra programs).
+        # event_id → list of EVENT programs *and* WHEN-headed clausal
+        # chains subscribed to it. Built lazily in start().
         self._event_table: dict[int, list[Program]] = {}
+        self._when_chain_table: dict[int, list[ClausalChain]] = {}
+        # External hook (defaults to "all conditions pass") for evaluating
+        # AND/OR records. Tests / HA replace this to model real state.
+        self._condition_evaluator = self._default_condition_evaluator
         self.metrics = _EngineMetrics()
 
+    @property
+    def chains(self) -> tuple[ClausalChain, ...]:
+        """All clausal chains decoded from the panel's program table."""
+        return self._chains
+
+    def set_condition_evaluator(self, fn) -> None:
+        """Replace the AND/OR condition evaluator.
+
+        ``fn`` is called with each AND/OR program record and must return
+        bool. The default returns True for every AND, False for every
+        OR (a degenerate evaluator that means "all chains' first AND
+        groups always pass" — useful as a smoke-test default, not for
+        real automation). Real callers supply a state-aware evaluator.
+        """
+        self._condition_evaluator = fn
+
+    @staticmethod
+    def _default_condition_evaluator(condition: Program) -> bool:
+        """Stub evaluator — caller should override via set_condition_evaluator."""
+        return condition.prog_type == int(ProgramType.AND)
+
     # ---- inspection -------------------------------------------------------
 
     @property
@@ -591,6 +745,30 @@ class ProgramEngine:
         self._event_table.clear()
         for program in self._classified.event:
             self._event_table.setdefault(program.event_id, []).append(program)
+        # Phase 5: clausal chains. AT and EVERY chains spawn worker
+        # tasks; WHEN chains register in a parallel event-dispatch table
+        # so emit_event() fires both raw EVENT programs and matching
+        # WHEN chains.
+        self._when_chain_table.clear()
+        for chain in self._chains:
+            if chain.head.prog_type == int(ProgramType.WHEN):
+                self._when_chain_table.setdefault(
+                    chain.head.event_id, []
+                ).append(chain)
+            elif chain.head.prog_type == int(ProgramType.AT):
+                self._tasks.append(
+                    asyncio.create_task(
+                        self._run_at_chain(chain),
+                        name=f"omni-pca-at-chain-{chain.head.slot}",
+                    )
+                )
+            elif chain.head.prog_type == int(ProgramType.EVERY):
+                self._tasks.append(
+                    asyncio.create_task(
+                        self._run_every_chain(chain),
+                        name=f"omni-pca-every-chain-{chain.head.slot}",
+                    )
+                )
 
     async def _run_timed_program(self, program: Program) -> None:
         """Sleep-until-next-fire loop for one TIMED program.
@@ -647,7 +825,12 @@ class ProgramEngine:
         programs = self._event_table.get(event_id, ())
         for program in programs:
             await self._fire(program)
-        return len(programs)
+        fired = len(programs)
+        # Plus any WHEN-headed clausal chains subscribed to this event.
+        for chain in self._when_chain_table.get(event_id, ()):
+            if await self._fire_chain(chain):
+                fired += 1
+        return fired
 
     async def emit_user_macro_button(self, button: int) -> int:
         """Convenience: fire EVENT programs subscribed to a button press."""
@@ -684,6 +867,82 @@ class ProgramEngine:
             )
             self.metrics.errors += 1
 
+    async def _fire_chain(self, chain: ClausalChain) -> bool:
+        """Evaluate a chain's AND/OR conditions; if they pass, fire every
+        THEN action. Returns True iff the conditions passed.
+
+        Each fired THEN action goes through the same wire-handler path
+        as TIMED/YEARLY/EVENT programs.
+        """
+        try:
+            passed = evaluate_conditions(
+                chain.conditions, is_satisfied=self._condition_evaluator,
+            )
+        except Exception:
+            _log.exception(
+                "engine: chain %s condition evaluation raised",
+                chain.head.slot,
+            )
+            self.metrics.errors += 1
+            return False
+        if not passed:
+            return False
+        for action in chain.actions:
+            await self._fire(action)
+        return True
+
+    async def _run_at_chain(self, chain: ClausalChain) -> None:
+        """Sleep-until-next-fire loop for an AT-headed chain.
+
+        AT records carry the same TIMED fields (hour/minute/days/
+        time_kind/time_offset) as compact-form TIMED programs, so we
+        reuse the same scheduling primitives.
+        """
+        try:
+            while self._running:
+                now = self._clock.now()
+                head = chain.head
+                if head.time_kind == TimeKind.ABSOLUTE:
+                    next_fire = _next_absolute_fire(now, head)
+                elif self._location is None:
+                    return
+                else:
+                    next_fire = _next_sun_relative_fire(now, head, self._location)
+                if next_fire is None:
+                    return
+                await self._clock.sleep_until(next_fire)
+                if not self._running:
+                    return
+                await self._fire_chain(chain)
+        except asyncio.CancelledError:
+            raise
+        except Exception:
+            _log.exception("engine: AT chain slot %s crashed", chain.head.slot)
+            self.metrics.errors += 1
+
+    async def _run_every_chain(self, chain: ClausalChain) -> None:
+        """Sleep-until-next-fire loop for an EVERY-headed chain.
+
+        Interval is in seconds per :meth:`Program.every_interval`. Zero
+        disables the chain (matches real-panel behaviour for an
+        unconfigured EVERY record).
+        """
+        interval_sec = chain.head.every_interval
+        if interval_sec <= 0:
+            return
+        delay = timedelta(seconds=interval_sec)
+        try:
+            while self._running:
+                await self._clock.sleep_until(self._clock.now() + delay)
+                if not self._running:
+                    return
+                await self._fire_chain(chain)
+        except asyncio.CancelledError:
+            raise
+        except Exception:
+            _log.exception("engine: EVERY chain slot %s crashed", chain.head.slot)
+            self.metrics.errors += 1
+
     async def _fire(self, program: Program) -> None:
         """Execute one program by feeding its command through the same
         wire-handler path the v2 Command opcode uses."""
diff --git a/tests/test_program_engine.py b/tests/test_program_engine.py
index 0f53a47..18fd07a 100644
--- a/tests/test_program_engine.py
+++ b/tests/test_program_engine.py
@@ -140,21 +140,22 @@ def _yearly(slot: int) -> Program:
     )
 
 
-def _when(slot: int) -> Program:
+def _bare_when(slot: int) -> Program:
     return Program(slot=slot, prog_type=int(ProgramType.WHEN), cond=0x0001)
 
 
-def _and(slot: int) -> Program:
+def _bare_and(slot: int) -> Program:
     return Program(slot=slot, prog_type=int(ProgramType.AND))
 
 
-def _then(slot: int) -> Program:
+def _bare_then(slot: int) -> Program:
     return Program(slot=slot, prog_type=int(ProgramType.THEN), cmd=3)
 
 
 def test_classify_buckets_each_type() -> None:
     bag = (
-        _free(), _timed(2), _event(3), _yearly(4), _when(5), _and(6), _then(7),
+        _free(), _timed(2), _event(3), _yearly(4),
+        _bare_when(5), _bare_and(6), _bare_then(7),
     )
     out = classify(bag)
     assert [p.slot for p in out.timed] == [2]
@@ -206,7 +207,7 @@ async def test_engine_constructs_against_empty_panel() -> None:
 
 @pytest.mark.asyncio
 async def test_engine_classifies_loaded_programs() -> None:
-    panel = _panel_with_programs(_timed(1), _event(2), _yearly(3), _when(4))
+    panel = _panel_with_programs(_timed(1), _event(2), _yearly(3), _bare_when(4))
     engine = ProgramEngine(panel, clock=FakeClock(
         datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
     ))
@@ -772,3 +773,247 @@ async def test_engine_fires_sun_relative_program_with_location() -> None:
         await asyncio.sleep(0)
         assert engine.metrics.timed_fired == 1
         assert panel.state.units[5].state == 1
+
+
+# ---- Phase 5: Clausal chains --------------------------------------------
+
+
+from omni_pca.program_engine import (  # noqa: E402
+    ClausalChain,
+    build_chains,
+    evaluate_conditions,
+)
+
+
+def _when(slot: int, event_id: int) -> Program:
+    return Program(
+        slot=slot, prog_type=int(ProgramType.WHEN),
+        month=(event_id >> 8) & 0xFF, day=event_id & 0xFF,
+    )
+
+
+def _at(slot: int, hour: int, minute: int, days: int) -> Program:
+    return Program(
+        slot=slot, prog_type=int(ProgramType.AT),
+        hour=hour, minute=minute, days=days,
+    )
+
+
+def _every(slot: int, interval_sec: int) -> Program:
+    # every_interval = ((cond & 0xFF) << 8) | ((cond2 >> 8) & 0xFF)
+    cond = (interval_sec >> 8) & 0xFF
+    cond2 = (interval_sec & 0xFF) << 8
+    return Program(
+        slot=slot, prog_type=int(ProgramType.EVERY),
+        cond=cond, cond2=cond2,
+    )
+
+
+def _and_cond(slot: int) -> Program:
+    return Program(slot=slot, prog_type=int(ProgramType.AND))
+
+
+def _or_cond(slot: int) -> Program:
+    return Program(slot=slot, prog_type=int(ProgramType.OR))
+
+
+def _then_action(slot: int, cmd: int, pr2: int) -> Program:
+    return Program(
+        slot=slot, prog_type=int(ProgramType.THEN),
+        cmd=cmd, pr2=pr2,
+    )
+
+
+def test_build_chains_simple_when_then() -> None:
+    """Minimal chain: WHEN at slot 1, THEN at slot 2."""
+    chains = build_chains((
+        _when(1, 0x0405),
+        _then_action(2, int(Command.UNIT_ON), 7),
+    ))
+    assert len(chains) == 1
+    assert chains[0].head.slot == 1
+    assert chains[0].conditions == ()
+    assert [a.slot for a in chains[0].actions] == [2]
+
+
+def test_build_chains_with_and_conditions_and_multiple_actions() -> None:
+    chains = build_chains((
+        _when(1, 0x0405),
+        _and_cond(2),
+        _and_cond(3),
+        _then_action(4, int(Command.UNIT_ON), 1),
+        _then_action(5, int(Command.UNIT_OFF), 2),
+    ))
+    assert len(chains) == 1
+    c = chains[0]
+    assert [x.slot for x in c.conditions] == [2, 3]
+    assert [a.slot for a in c.actions] == [4, 5]
+
+
+def test_build_chains_separates_adjacent_chains() -> None:
+    chains = build_chains((
+        _when(1, 0x0405),
+        _then_action(2, 1, 1),
+        _at(3, 6, 0, int(Days.MONDAY)),
+        _then_action(4, 1, 2),
+    ))
+    assert [c.head.slot for c in chains] == [1, 3]
+    assert chains[0].actions[0].slot == 2
+    assert chains[1].actions[0].slot == 4
+
+
+def test_build_chains_drops_chains_without_then() -> None:
+    """A WHEN with no THEN has nothing to fire — skip silently."""
+    chains = build_chains((
+        _when(1, 0x0405),
+        _and_cond(2),
+        # no THEN
+    ))
+    assert chains == ()
+
+
+def test_build_chains_stops_at_non_clausal_record() -> None:
+    """A TIMED record between chains ends the prior chain."""
+    timed = Program(
+        slot=3, prog_type=int(ProgramType.TIMED),
+        cmd=1, hour=6, minute=0, days=int(Days.MONDAY),
+    )
+    chains = build_chains((
+        _when(1, 0x0405),
+        _then_action(2, 1, 1),
+        timed,
+        _when(4, 0x0410),
+        _then_action(5, 1, 2),
+    ))
+    assert [c.head.slot for c in chains] == [1, 4]
+
+
+def test_evaluate_conditions_empty_is_true() -> None:
+    assert evaluate_conditions((), is_satisfied=lambda c: False) is True
+
+
+def test_evaluate_conditions_all_ands() -> None:
+    cs = (_and_cond(1), _and_cond(2))
+    assert evaluate_conditions(cs, is_satisfied=lambda c: True) is True
+    assert evaluate_conditions(cs, is_satisfied=lambda c: False) is False
+    # One fails → whole group fails.
+    assert evaluate_conditions(
+        cs, is_satisfied=lambda c: c.slot == 1,
+    ) is False
+
+
+def test_evaluate_conditions_or_group_separation() -> None:
+    """Two groups via OR: group A (AND only) fails, group B (OR + AND) passes."""
+    cs = (
+        _and_cond(1),  # group A start
+        _and_cond(2),
+        _or_cond(3),  # group B start (OR record itself)
+        _and_cond(4),
+    )
+    # Group A: slots 1, 2; Group B: slots 3, 4.
+    def is_sat(c):
+        return c.slot in (3, 4)  # group B fully passes
+    assert evaluate_conditions(cs, is_satisfied=is_sat) is True
+
+
+@pytest.mark.asyncio
+async def test_engine_classifies_clausal_heads() -> None:
+    """Engine exposes built chains via the chains property."""
+    panel = _panel_with_programs(
+        _when(1, 0x0405),
+        _then_action(2, int(Command.UNIT_ON), 7),
+    )
+    engine = ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    ))
+    assert len(engine.chains) == 1
+
+
+@pytest.mark.asyncio
+async def test_engine_when_chain_fires_on_event() -> None:
+    """A WHEN-headed chain dispatches when emit_event() matches its event."""
+    button_evt = event_id_user_macro_button(7)
+    panel = _panel_with_programs(
+        _when(1, button_evt),
+        _then_action(2, int(Command.UNIT_ON), 9),
+    )
+    async with ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    )) as engine:
+        fired = await engine.emit_user_macro_button(7)
+        assert fired == 1
+        assert engine.metrics.clausal_fired == 1
+        assert panel.state.units[9].state == 1
+
+
+@pytest.mark.asyncio
+async def test_engine_when_chain_blocked_by_failing_condition() -> None:
+    """Default condition evaluator passes ANDs but fails ORs. A chain
+    with one AND condition fires; a chain with an OR-only group doesn't."""
+    button_evt = event_id_user_macro_button(7)
+    panel = _panel_with_programs(
+        _when(1, button_evt),
+        _and_cond(2),
+        _then_action(3, int(Command.UNIT_ON), 9),
+    )
+    async with ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    )) as engine:
+        # Default evaluator: ANDs pass → chain runs.
+        fired = await engine.emit_user_macro_button(7)
+        assert fired == 1
+        assert panel.state.units[9].state == 1
+
+
+@pytest.mark.asyncio
+async def test_engine_custom_evaluator_can_block_chain() -> None:
+    """Replace evaluator with always-False; chain doesn't fire."""
+    button_evt = event_id_user_macro_button(7)
+    panel = _panel_with_programs(
+        _when(1, button_evt),
+        _and_cond(2),
+        _then_action(3, int(Command.UNIT_ON), 9),
+    )
+    async with ProgramEngine(panel, clock=FakeClock(
+        datetime(2026, 5, 14, 0, 0, tzinfo=timezone.utc)
+    )) as engine:
+        engine.set_condition_evaluator(lambda c: False)
+        fired = await engine.emit_user_macro_button(7)
+        # Returns 0 — the chain matched the event but failed conditions.
+        assert fired == 0
+        assert engine.metrics.clausal_fired == 0
+
+
+@pytest.mark.asyncio
+async def test_engine_at_chain_fires_at_scheduled_time() -> None:
+    """AT-headed chain fires at hour:minute on matching days."""
+    t0 = datetime(2026, 5, 11, 5, 59, tzinfo=timezone.utc)  # Mon 05:59
+    panel = _panel_with_programs(
+        _at(1, hour=6, minute=0, days=int(Days.MONDAY)),
+        _then_action(2, int(Command.UNIT_ON), 7),
+    )
+    clock = FakeClock(t0)
+    async with ProgramEngine(panel, clock=clock) as engine:
+        await asyncio.sleep(0)
+        await clock.advance_to(t0 + timedelta(minutes=2))
+        await asyncio.sleep(0)
+        assert engine.metrics.clausal_fired == 1
+        assert panel.state.units[7].state == 1
+
+
+@pytest.mark.asyncio
+async def test_engine_every_chain_fires_on_interval() -> None:
+    """EVERY chain fires every N seconds."""
+    t0 = datetime(2026, 5, 14, 12, 0, tzinfo=timezone.utc)
+    panel = _panel_with_programs(
+        _every(1, interval_sec=60),
+        _then_action(2, int(Command.UNIT_ON), 7),
+    )
+    clock = FakeClock(t0)
+    async with ProgramEngine(panel, clock=clock) as engine:
+        await asyncio.sleep(0)
+        # Walk three intervals.
+        for tick in (1, 2, 3):
+            await clock.advance_to(t0 + timedelta(seconds=60 * tick + 1))
+            await asyncio.sleep(0)
+        assert engine.metrics.clausal_fired == 3