diff --git a/docs/implementation-plan.md b/docs/implementation-plan.md
index fa9fbd5..5658201 100644
--- a/docs/implementation-plan.md
+++ b/docs/implementation-plan.md
@@ -25,6 +25,8 @@ shape removes independent per-kind storage from the live foundation.
     Aquarium/Faust C ABI: opaque reservoir create/destroy, sample-handle push,
     edge/window queries, ring counts, and latest sample lookup by sensor hash.
     The ABI now exposes total rolling-buffer length and typed-view length.
+  - `localcast_hash_source_id` owns stable FNV-1a source hashing for native
+    producers; empty/null source ids produce zero and are rejected.
   - `LocalcastRuntime` wraps the current reservoir with typed native producer
     calls and total/typed read functions. It is the intended live spine for
     Aquarium/Faust bindings.
@@ -134,9 +136,10 @@ shape removes independent per-kind storage from the live foundation.
    packet handles through `ILocalCastNativeRuntime` with an injected payload
    decoder. It also has the matching safe-code audio block and render packet
    descriptor bindings, plus a render descriptor decoder that reads timing and
-   target metadata from native payload handles while leaving point-buffer
-   decoding injectable. The next Aquarium cut is wiring native runtime creation
-   and real point-buffer decode into the app path.
+   target metadata from native payload handles and decodes the first native
+   point-buffer ABI. Aquarium also exposes the native source-id hash wrapper.
+   The next Aquarium cut is wiring native runtime creation into the app path
+   once a producer exists to feed it.
 3. Move camera/mic/loopback ingest into native capture workers that use
    `LocalcastProducer` to append typed sample handles.
 4. Move feature extraction, flow, cross-view matching, LOD reconciliation,
diff --git a/native/README.md b/native/README.md
index 0eb91d3..df6fc11 100644
--- a/native/README.md
+++ b/native/README.md
@@ -19,6 +19,9 @@ tests, and offline analysis. It does not own dense live fusion or DSP.
 The reservoir ABI is intentionally small:
 
 - `LocalcastReservoir` is opaque.
+- `localcast_hash_source_id` is the stable FNV-1a source-id hash used before
+  creating producers. Empty or null source ids hash to zero and are rejected by
+  producer creation.
 - `LocalcastSampleHandle` is sample metadata plus a `payload_handle` and
   provenance flags. Live samples must have `flags == 0`; diagnostic or unknown
   flagged samples are rejected by the live reservoir.
diff --git a/native/reservoir/include/localcast_reservoir.h b/native/reservoir/include/localcast_reservoir.h
index 451ffaf..5d81ad1 100644
--- a/native/reservoir/include/localcast_reservoir.h
+++ b/native/reservoir/include/localcast_reservoir.h
@@ -94,6 +94,8 @@ typedef struct LocalcastRuntimeStatus {
     size_t render_packet_count;
 } LocalcastRuntimeStatus;
 
+uint64_t localcast_hash_source_id(const uint8_t *bytes, size_t byte_len);
+
 LocalcastReservoir *localcast_reservoir_create(uint64_t duration_ns);
 void localcast_reservoir_destroy(LocalcastReservoir *reservoir);
 
diff --git a/native/reservoir/src/lib.rs b/native/reservoir/src/lib.rs
index bc3322d..9804ad4 100644
--- a/native/reservoir/src/lib.rs
+++ b/native/reservoir/src/lib.rs
@@ -3,6 +3,8 @@ use std::collections::VecDeque;
 pub const DEFAULT_RESERVOIR_NS: u64 = 5_000_000_000;
 pub const LOCALCAST_SAMPLE_FLAG_DIAGNOSTIC: u32 = 1 << 0;
 pub const LOCALCAST_AUDIO_SAMPLE_FORMAT_F32_INTERLEAVED: u32 = 1;
+const FNV1A_OFFSET_64: u64 = 14_695_981_039_346_656_037;
+const FNV1A_PRIME_64: u64 = 1_099_511_628_211;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub enum SampleKind {
@@ -357,6 +359,29 @@ fn is_live_sample(sample: LocalcastSampleHandle) -> bool {
     sample.flags == 0
 }
 
+fn hash_source_id(bytes: &[u8]) -> u64 {
+    if bytes.is_empty() {
+        return 0;
+    }
+    let mut hash = FNV1A_OFFSET_64;
+    for byte in bytes {
+        hash ^= u64::from(*byte);
+        hash = hash.wrapping_mul(FNV1A_PRIME_64);
+    }
+    if hash == 0 { 1 } else { hash }
+}
+
+#[unsafe(no_mangle)]
+pub extern "C" fn localcast_hash_source_id(bytes: *const u8, byte_len: usize) -> u64 {
+    if byte_len == 0 {
+        return 0;
+    }
+    if bytes.is_null() {
+        return 0;
+    }
+    hash_source_id(unsafe { std::slice::from_raw_parts(bytes, byte_len) })
+}
+
 #[unsafe(no_mangle)]
 pub extern "C" fn localcast_reservoir_create(duration_ns: u64) -> *mut LocalcastReservoir {
     Box::into_raw(Box::new(LocalcastReservoir {
@@ -923,6 +948,19 @@ mod tests {
         }
     }
 
+    #[test]
+    fn source_id_hash_is_stable_and_rejects_empty_sources() {
+        let source = b"kiyo-primary";
+
+        assert_eq!(0, hash_source_id(b""));
+        assert_eq!(0, localcast_hash_source_id(std::ptr::null(), source.len()));
+        assert_eq!(
+            hash_source_id(source),
+            localcast_hash_source_id(source.as_ptr(), source.len())
+        );
+        assert_ne!(hash_source_id(source), hash_source_id(b"kiyo-secondary"));
+    }
+
     #[test]
     fn rolling_reservoir_expires_every_kind_from_one_edge() {
         let mut reservoir = RollingReservoir::new(DEFAULT_RESERVOIR_NS);
diff --git a/notes/fresh-workspace-handoff.md b/notes/fresh-workspace-handoff.md
index aca358c..3de2359 100644
--- a/notes/fresh-workspace-handoff.md
+++ b/notes/fresh-workspace-handoff.md
@@ -33,6 +33,8 @@ Get-Content .\state\evidence.jsonl -Tail 8
 - `LocalcastRuntime` now exposes producer pushes and consumer reads.
   `LocalcastProducer` owns source identity and sequence assignment for native
   capture workers.
+- `localcast_hash_source_id` owns stable FNV-1a source-id hashing for native
+  producer creation.
 - `LocalcastAudioBlockDescriptor` is the first typed audio payload descriptor:
   caller-owned float32 interleaved audio blocks cross the ABI by descriptor
   pointer, while the reservoir still owns only timing/retention metadata.
@@ -58,6 +60,10 @@ Get-Content .\state\evidence.jsonl -Tail 8
 - Aquarium-Engine commit `cfb48d7` adds `LocalCastNativeRenderDescriptorDecoder`,
   which reads render descriptor timing/target metadata from native payload
   handles while keeping point-buffer decoding injectable.
+- Aquarium-Engine commit `f4c5988` adds `LocalCastNativeRenderPoint` and native
+  point-buffer decoding for the render descriptor decoder.
+- Aquarium-Engine commit `924aa2f` exposes `LocalCastNativeSourceId.HashUtf8`
+  as the safe wrapper over native source-id hashing.
 - Edge JSON is schema/diagnostic only. Runtime network/process data should remain typed CultNet documents.
 - Python live producers and diagnostic CultCache/JSON file adapters are
   diagnostics, not production foundations. The OpenGL Spout sink has been
diff --git a/state/evidence.jsonl b/state/evidence.jsonl
index bc562e8..0e56a09 100644
--- a/state/evidence.jsonl
+++ b/state/evidence.jsonl
@@ -83,3 +83,6 @@
 {"ts": "2026-05-19T11:21:55+00:00", "type": "implementation", "status": "ok", "note": "Aquarium-Engine commit cfb48d7 adds LocalCastNativeRenderDescriptorDecoder: Aquarium now reads LocalcastRenderPacketDescriptor timing/target metadata from native payload handles while keeping point-buffer decoding as an injected boundary."}
 {"ts": "2026-05-19T11:25:11+00:00", "type": "decision", "status": "ok", "note": "Mimir is now the public brand for the LocalCastBridge/localcast implementation surfaces: local sensors become one coherent realtime volumetric field, while OBS, Aquarium, Faust, and FFmpeg retain their existing ownership boundaries."}
 {"ts": "2026-05-19T11:25:59+00:00", "type": "implementation", "status": "ok", "note": "Native reservoir ABI now includes LocalcastRenderPoint, the fixed first point-buffer element for Aquarium render decoding: stable-key hash, source timestamp, position, radius, color/alpha, and confidence."}
+{"ts": "2026-05-19T11:29:24+00:00", "type": "implementation", "status": "ok", "note": "Aquarium-Engine commit f4c5988 adds LocalCastNativeRenderPoint binding plus native point-buffer decoding for LocalCastNativeRenderDescriptorDecoder; LocalCast tests pass 20 tests no-build."}
+{"ts": "2026-05-19T11:30:58+00:00", "type": "implementation", "status": "ok", "note": "Native reservoir ABI now owns source-id hashing through localcast_hash_source_id, a stable FNV-1a hash for producer source identity; null/empty sources hash to zero and producer creation still rejects zero."}
+{"ts": "2026-05-19T11:34:44+00:00", "type": "implementation", "status": "ok", "note": "Aquarium-Engine commit 924aa2f exposes LocalCastNativeSourceId.HashUtf8 as a safe wrapper over native localcast_hash_source_id, avoiding managed reimplementation of source identity hashing."}
diff --git a/state/map.yaml b/state/map.yaml
index c62cd89..227b7c5 100644
--- a/state/map.yaml
+++ b/state/map.yaml
@@ -56,6 +56,8 @@ accepted_design:
   - `LocalcastRuntime` exposes typed producer pushes plus total/typed window
     reads. `LocalcastProducer` owns source identity and sequence assignment
     before hardware adapters append live sample handles.
+  - `localcast_hash_source_id` owns stable native source-id hashing so capture
+    workers do not each invent incompatible sensor hashes.
   - `LocalcastAudioBlockDescriptor` is the first typed payload descriptor for
     caller-owned float32 interleaved audio blocks; the reservoir stores only the
     descriptor pointer as a payload handle and does not own DSP memory.