fix(agent): persist behavioural config; make compression actually work

Eight MemoryConfig fields (float16, compression, compression_level,
compact_threshold, hebbian_boost, decay_factor, wal_enabled, wal_max_entries)
were never written to /meta, so reopening a store silently reset them to
defaults — a compressed store was rewritten uncompressed by the first
checkpoint after a reopen, and wal_enabled=false flipped back to true. They
are now stored as /meta attributes; each is optional on load so older files
keep opening with the previous defaults, and non-finite floats are ignored.

Writing the round-trip test exposed that `compression = true` never worked in
a default build: the embeddings dataset called with_zstd() unconditionally but
the agent crate never enabled the zstd feature, so every checkpoint failed
with "unsupported filter: 32015". The default build now compresses with
deflate (always available, pure Rust path); Zstd is opt-in via a new `zstd`
agent feature.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

crates/clawhdf5-agent/Cargo.toml

@@ -48,6 +48,9 @@ harness = false
 default = ["float16", "hnsw"]
 float16 = ["half"]
 parallel = ["rayon"]
+# Compress embeddings with Zstd instead of deflate when
+# `MemoryConfig::compression` is on. Off by default: it links libzstd (C).
+zstd = ["clawhdf5/zstd"]
 # HNSW approximate-nearest-neighbour acceleration for the vector stage of
 # hybrid_search. On by default; the index is rebuilt from the cache on demand
 # and stays self-consistent with the persisted memory store. Disable with

crates/clawhdf5-agent/src/schema.rs

@@ -54,6 +54,27 @@ pub fn build_hdf5_file_with_mark(
     meta.set_attr("embedding_dim", AttrValue::I64(config.embedding_dim as i64));
     meta.set_attr("chunk_size", AttrValue::I64(config.chunk_size as i64));
     meta.set_attr("overlap", AttrValue::I64(config.overlap as i64));
+    // Behavioural settings. These used to live only in memory, so reopening a
+    // store silently reset them to defaults — e.g. a compressed store was
+    // rewritten uncompressed by the first checkpoint after a reopen. Loaders
+    // treat each one as optional so older files keep opening.
+    meta.set_attr("float16", AttrValue::I64(config.float16.into()));
+    meta.set_attr("compression", AttrValue::I64(config.compression.into()));
+    meta.set_attr(
+        "compression_level",
+        AttrValue::I64(config.compression_level.into()),
+    );
+    meta.set_attr(
+        "compact_threshold",
+        AttrValue::F64(config.compact_threshold.into()),
+    );
+    meta.set_attr("hebbian_boost", AttrValue::F64(config.hebbian_boost.into()));
+    meta.set_attr("decay_factor", AttrValue::F64(config.decay_factor.into()));
+    meta.set_attr("wal_enabled", AttrValue::I64(config.wal_enabled.into()));
+    meta.set_attr(
+        "wal_max_entries",
+        AttrValue::I64(config.wal_max_entries as i64),
+    );
     meta.set_attr(
         "edgehdf5_version",
         AttrValue::String(ZEROCLAW_VERSION.into()),
@@ -107,15 +128,33 @@ fn build_memory_group(
             let rows_per_chunk = (target_chunk_bytes / (d * 4)).max(1).min(n);
             ds.with_chunks(&[rows_per_chunk, d]);
 
-            // Compression: Zstd for embeddings — faster than deflate at same ratio.
-            // Shuffle is applied automatically (auto-shuffle pre-filter).
+            // Compression. Shuffle is applied automatically (auto-shuffle
+            // pre-filter). Zstd is faster than deflate at the same ratio but
+            // pulls in libzstd, so it is opt-in via the `zstd` feature; the
+            // default build uses deflate, which is always available. (This
+            // used to call `with_zstd` unconditionally, so without the
+            // feature every checkpoint of a compressed store failed with
+            // "unsupported filter: 32015".) Both are standard HDF5 filters;
+            // reading a zstd-compressed store needs a zstd-enabled build.
             if config.compression {
-                let level = if config.compression_level > 0 {
-                    config.compression_level.min(22)
-                } else {
-                    3 // Zstd level 3: fast + good ratio for f32 embeddings
-                };
-                ds.with_zstd(level);
+                #[cfg(feature = "zstd")]
+                {
+                    let level = if config.compression_level > 0 {
+                        config.compression_level.min(22)
+                    } else {
+                        3 // fast + good ratio for f32 embeddings
+                    };
+                    ds.with_zstd(level);
+                }
+                #[cfg(not(feature = "zstd"))]
+                {
+                    let level = if config.compression_level > 0 {
+                        config.compression_level.min(9)
+                    } else {
+                        4
+                    };
+                    ds.with_deflate(level);
+                }
             }
         }
 
@@ -382,15 +421,19 @@ pub fn validate_and_load(
         embedding_dim,
         chunk_size,
         overlap,
-        float16: false,
-        compression: false,
-        compression_level: 0,
-        compact_threshold: 0.3,
-        hebbian_boost: 0.15,
-        decay_factor: 0.98,
+        float16: optional_bool_attr(&attrs, "float16", false),
+        compression: optional_bool_attr(&attrs, "compression", false),
+        compression_level: optional_i64_attr(&attrs, "compression_level")
+            .and_then(|v| u32::try_from(v).ok())
+            .unwrap_or(0),
+        compact_threshold: optional_f32_attr(&attrs, "compact_threshold", 0.3),
+        hebbian_boost: optional_f32_attr(&attrs, "hebbian_boost", 0.15),
+        decay_factor: optional_f32_attr(&attrs, "decay_factor", 0.98),
         created_at,
-        wal_enabled: true,
-        wal_max_entries: 500,
+        wal_enabled: optional_bool_attr(&attrs, "wal_enabled", true),
+        wal_max_entries: optional_i64_attr(&attrs, "wal_max_entries")
+            .and_then(|v| usize::try_from(v).ok())
+            .unwrap_or(500),
     };
 
     // Load /memory group
@@ -595,6 +638,27 @@ fn extract_string_attr(
     }
 }
 
+type MetaAttrs = std::collections::HashMap<String, AttrValue>;
+
+fn optional_i64_attr(attrs: &MetaAttrs, name: &str) -> Option<i64> {
+    match attrs.get(name) {
+        Some(AttrValue::I64(v)) => Some(*v),
+        _ => None,
+    }
+}
+
+fn optional_bool_attr(attrs: &MetaAttrs, name: &str, default: bool) -> bool {
+    optional_i64_attr(attrs, name).map_or(default, |v| v != 0)
+}
+
+/// Finite values only: a NaN threshold/decay would poison every comparison.
+fn optional_f32_attr(attrs: &MetaAttrs, name: &str, default: f32) -> f32 {
+    match attrs.get(name) {
+        Some(AttrValue::F64(v)) if v.is_finite() => *v as f32,
+        _ => default,
+    }
+}
+
 fn extract_i64_attr(
     attrs: &std::collections::HashMap<String, AttrValue>,
     name: &str,
@@ -716,6 +780,36 @@ mod tests {
         validate_and_load(&file).map(|(_, cache, _, _)| cache)
     }
 
+    #[test]
+    fn behavioural_config_survives_a_reopen() {
+        let mut cfg = config();
+        cfg.compression = true;
+        cfg.compression_level = 7;
+        cfg.compact_threshold = 0.5;
+        cfg.hebbian_boost = 0.25;
+        cfg.decay_factor = 0.9;
+        cfg.wal_enabled = false;
+        cfg.wal_max_entries = 42;
+        let bytes = build_hdf5_file(
+            &cfg,
+            &cache_with(2),
+            &SessionCache::new(),
+            &KnowledgeCache::new(),
+        )
+        .unwrap();
+        let file = clawhdf5::File::from_bytes(bytes).unwrap();
+        let (loaded, loaded_cache, ..) = validate_and_load(&file).unwrap();
+        // The compressed embeddings must also read back intact.
+        assert_eq!(loaded_cache.embeddings, cache_with(2).embeddings);
+        assert!(loaded.compression);
+        assert_eq!(loaded.compression_level, 7);
+        assert_eq!(loaded.compact_threshold, 0.5);
+        assert_eq!(loaded.hebbian_boost, 0.25);
+        assert_eq!(loaded.decay_factor, 0.9);
+        assert!(!loaded.wal_enabled);
+        assert_eq!(loaded.wal_max_entries, 42);
+    }
+
     #[test]
     fn consistent_store_loads() {
         let loaded = roundtrip(&cache_with(3)).unwrap();