feat(#18): affect.fetch — adopt bifrost 0.10.0 mandatory fetch (D1 prerequisite)

bifrost 0.10.0's _supports_affect_plane (bifrost/affect.py:75-80) now requires a
callable fetch for the affect capability to advertise/dispatch at all (INV-012
strong-or-absent), so an emit-only store 400s on EVERY affect op — repinning past
the affect.fetch release (#12/#13) breaks our shipped affect plane until fetch
exists. Implement affect.fetch as a thin async wrapper over the existing get()
read seam, conformed verbatim to the reference InMemoryAffectStore.fetch:
{"found": False} or {"found": True, "snapshot": <verbatim>}, AffectInvalidArguments
on empty ids, opaque (INV-001 — never reads pad/valence).

This is the forced prerequisite for the #18 D1 composite (build_combined_app),
and a new Worldtree I/O point consumed (affect read-back over bifrost).

- Repin bifrost>=0.8.0 -> >=0.10.0 (uv lock: 0.8.0 -> 0.10.0)
- affect_store.py: add async fetch() over get()
- contract bifrost_affect_provider v1.2: fetch FN block + INV-010 (cap = supported+emit+fetch)
- tests: 3 fetch unit + parity_vs_reference_fetch through dispatch_affect_call
- suite 482 -> 486 green

tests/test_provider_affect.py

@@ -162,6 +162,32 @@ async def test_get_after_emit_returns_equal():
     assert store.get("a1", "u1") == snap
 
 
+# --- fetch (affect.fetch wire verb — bifrost >=0.10.0, INV-010 strong-or-absent) ---
+
+async def test_fetch_absent_returns_found_false():
+    """fetch_absent: no row for the key → {"found": False} (mirrors reference)."""
+    store = open_affect_store(":memory:")
+    assert await store.fetch("nope", "nope") == {"found": False}
+
+
+async def test_fetch_after_emit_returns_snapshot():
+    """fetch_after_emit [tracer]: emit then fetch → {"found": True, "snapshot": <verbatim>}."""
+    store = open_affect_store(":memory:")
+    snap = _snapshot()
+    await store.emit(snap, idempotency_key="k1", ctx=_ctx())
+    assert await store.fetch("a1", "u1") == {"found": True, "snapshot": snap}
+
+
+async def test_fetch_missing_key_raises():
+    """fetch_missing_key: empty/missing addressing key → AffectInvalidArguments
+    (PRE-001; symmetric across both keys, belt-and-suspenders behind the wire)."""
+    store = open_affect_store(":memory:")
+    with pytest.raises(AffectInvalidArguments):
+        await store.fetch("", "u1")
+    with pytest.raises(AffectInvalidArguments):
+        await store.fetch("a1", "")
+
+
 # --- build_affect_provider_app ---
 
 def test_build_app_exposes_handshake_and_affect_routes():
@@ -243,6 +269,36 @@ async def test_parity_vs_reference_store_through_dispatch():
     )
 
 
+def _fetch_env(agent_id: str = "agent-1", end_user_id: str = "user-1") -> dict:
+    return {"operation": "affect.fetch", "args": {"agent_id": agent_id, "end_user_id": end_user_id}}
+
+
+async def test_parity_vs_reference_fetch_through_dispatch():
+    """#195 parity for affect.fetch: cold (not-found) + warm (found) read envelopes
+    yield identical (status, body) through the real engine against the reference store
+    and ours. Conforms to bifrost's InMemoryAffectStore.fetch ({found, snapshot})."""
+    from bifrost.affect import dispatch_affect_call
+    from bifrost.consumer.testing import InMemoryAffectStore
+
+    ref = InMemoryAffectStore()
+    mine = open_affect_store(":memory:")
+    write_ctx = _dispatch_ctx("affect:write")
+    read_ctx = _dispatch_ctx("affect:read")
+
+    # cold fetch (nothing persisted): both -> {found: false}
+    assert await dispatch_affect_call(_fetch_env(), read_ctx, ref) == await dispatch_affect_call(
+        _fetch_env(), read_ctx, mine
+    )
+
+    # seed both via emit, then fetch -> both {found: true, snapshot: <verbatim>}
+    snap = _ref_shaped_snapshot()
+    await dispatch_affect_call(_env(snap), write_ctx, ref)
+    await dispatch_affect_call(_env(snap), write_ctx, mine)
+    assert await dispatch_affect_call(_fetch_env(), read_ctx, ref) == await dispatch_affect_call(
+        _fetch_env(), read_ctx, mine
+    )
+
+
 # --- PAD read route (issue #18 Deliverable 2) ---
 # Non-bifrost GET /affect/state/{agent_id}?end_user_id=… → store.get snapshot.