diff --git a/crates/effects/src/plugin.rs b/crates/effects/src/plugin.rs
index 242f52b9..874050f4 100644
--- a/crates/effects/src/plugin.rs
+++ b/crates/effects/src/plugin.rs
@@ -137,6 +137,7 @@ pub struct PluginManifest {
 impl PluginManifest {
     /// Check the manifest against this API version.
     pub fn validate(&self) -> Result<(), String> {
+        const MAX_PARAMS: usize = 256;
         if self.api != PLUGIN_API_VERSION {
             return Err(format!("plug-in `{}` targets plug-in API {} but this build implements API {PLUGIN_API_VERSION}", self.id, self.api));
         }
@@ -147,6 +148,9 @@ impl PluginManifest {
         if self.name.trim().is_empty() || self.category.trim().is_empty() {
             return Err(format!("plug-in `{}` needs a name and a category", self.id));
         }
+        if self.params.len() > MAX_PARAMS {
+            return Err(format!("plug-in `{}` has {} parameters (at most {MAX_PARAMS})", self.id, self.params.len()));
+        }
         let mut seen = std::collections::HashSet::new();
         for p in &self.params {
             if p.id.is_empty() || !p.id.chars().all(|c| c.is_ascii_alphanumeric() || c == '_') || !seen.insert(p.id.as_str()) {
@@ -157,6 +161,12 @@ impl PluginManifest {
             {
                 return Err(format!("plug-in `{}`: popup `{}` needs options and a default index in range", self.id, p.id));
             }
+            if let PluginParamKind::Slider { default, min, max, slider_min, slider_max, .. } = &p.kind {
+                let (lo, hi) = (slider_min.unwrap_or(*min), slider_max.unwrap_or(*max));
+                if [*default, *min, *max, lo, hi].iter().any(|v| !v.is_finite()) || min > max || lo > hi || default < min || default > max {
+                    return Err(format!("plug-in `{}`: slider `{}` needs min ≤ default ≤ max (and sliderMin ≤ sliderMax)", self.id, p.id));
+                }
+            }
         }
         Ok(())
     }
diff --git a/crates/host/tests/plugins.rs b/crates/host/tests/plugins.rs
index c8a9b368..83891148 100644
--- a/crates/host/tests/plugins.rs
+++ b/crates/host/tests/plugins.rs
@@ -104,3 +104,58 @@ fn example_wasm_plugin_loads_and_renders() {
     let list = s.execute("effect.plugins.list", json!({})).unwrap();
     assert!(list["plugins"].as_array().unwrap().iter().any(|p| p["source"].as_str().unwrap_or("").ends_with(".wasm")));
 }
+
+/// A parameterless plug-in module (WebAssembly text): `render` is `ec_render`'s body.
+fn wat_plugin(id: &str, api: i32, render: &str) -> String {
+    let manifest = format!(r#"{{"api":1,"id":"{id}","name":"Host {id}","category":"Test Plug-ins","version":"1","params":[]}}"#);
+    let len = manifest.len();
+    let escaped = manifest.replace('"', "\\\"");
+    format!(
+        r#"(module
+  (memory (export "memory") 2)
+  (data (i32.const 16) "{escaped}")
+  (func (export "ec_api_version") (result i32) i32.const {api})
+  (func (export "ec_manifest_ptr") (result i32) i32.const 16)
+  (func (export "ec_manifest_len") (result i32) i32.const {len})
+  (func (export "ec_alloc") (param i32) (result i32) i32.const 1024)
+  (func (export "ec_render") (param i32 i32 i32 i32 i32 f64 f64) (result i32) {render}))"#
+    )
+}
+
+#[test]
+fn plugin_loading_reports_bad_modules_and_survives_failing_renders() {
+    let dir = std::env::temp_dir().join(format!("effectcraft-host-plugins-{}", std::process::id()));
+    std::fs::create_dir_all(&dir).unwrap();
+    let files = [
+        ("a-good.wasm", wat_plugin("org.test.host.good", 1, "i32.const 0").into_bytes()),
+        ("b-garbage.wasm", b"\0asm\x01\0\0\0garbage".to_vec()),
+        ("c-v2.wasm", wat_plugin("org.test.host.v2", 2, "i32.const 0").into_bytes()),
+        ("d-empty.wasm", vec![]),
+        ("e-trap.wasm", wat_plugin("org.test.host.trap", 1, "unreachable").into_bytes()),
+        ("notes.txt", b"not a plug-in".to_vec()),
+    ];
+    for (name, bytes) in &files {
+        std::fs::write(dir.join(name), bytes).unwrap();
+    }
+    let (mut s, l) = setup();
+    let r = s.execute("effect.plugins.load", json!({"folder": dir.to_string_lossy()})).unwrap();
+    let ids: Vec<&str> = r["loaded"].as_array().unwrap().iter().filter_map(|v| v["id"].as_str()).collect();
+    assert_eq!(ids, ["org.test.host.good", "org.test.host.trap"], "{r}");
+    let errs: Vec<String> = r["errors"].as_array().unwrap().iter().map(|e| e["path"].as_str().unwrap().to_string()).collect();
+    assert_eq!(errs.len(), 3, "{r}");
+    assert!(errs.iter().all(|p| !p.ends_with(".txt")));
+    assert!(r["errors"].to_string().contains("API 2"), "{r}");
+    // A single file: errors come back as command errors; loading twice is refused.
+    let good = dir.join("a-good.wasm").to_string_lossy().to_string();
+    assert!(s.execute("effect.plugins.load", json!({"path": good})).unwrap_err().to_string().contains("already registered"));
+    assert!(s.execute("effect.plugins.load", json!({"path": dir.join("missing.wasm").to_string_lossy()})).is_err());
+    assert!(s.execute("effect.plugins.load", json!({"folder": dir.join("missing").to_string_lossy()})).is_err());
+    assert!(s.execute("effect.plugins.load", json!({})).is_err());
+    // A plug-in that traps on every frame leaves the layer as it was.
+    let before = px(&s);
+    s.execute("effect.apply", json!({"layer": l, "effect": "org.test.host.trap"})).unwrap();
+    assert_eq!(px(&s), before);
+    s.execute("effect.apply", json!({"layer": l, "effect": "org.test.host.good"})).unwrap();
+    assert_eq!(px(&s), before);
+    let _ = std::fs::remove_dir_all(&dir);
+}
diff --git a/crates/plugin/src/tests.rs b/crates/plugin/src/tests.rs
index 9363ab3e..f68fde00 100644
--- a/crates/plugin/src/tests.rs
+++ b/crates/plugin/src/tests.rs
@@ -12,11 +12,20 @@ fn load_err(r: Result<&'static effectcraft_effects::EffectSpec, String>) -> Stri
     }
 }
 
+/// The gain plug-in's manifest.
+fn gain_manifest(id: &str) -> String {
+    format!(
+        r#"{{"api":1,"id":"{id}","name":"Gain {id}","category":"Test Plug-ins","version":"1.0","params":[{{"id":"gain","name":"Gain","type":"slider","default":0.5,"min":0,"max":4}},{{"id":"on","name":"Lift","type":"checkbox","default":false}},{{"id":"tint","name":"Tint","type":"color","default":[0,0,1,1]}}]}}"#
+    )
+}
+
 /// A plug-in in WebAssembly text: multiplies RGB by `gain`, adds `lift` × `tint` when `on`.
 fn gain_module(id: &str, render_body: &str) -> String {
-    let manifest = format!(
-        r#"{{"api":1,"id":"{id}","name":"Gain {id}","category":"Test Plug-ins","version":"1.0","params":[{{"id":"gain","name":"Gain","type":"slider","default":0.5,"min":0,"max":4}},{{"id":"on","name":"Lift","type":"checkbox","default":false}},{{"id":"tint","name":"Tint","type":"color","default":[0,0,1,1]}}]}}"#
-    );
+    module_with(&gain_manifest(id), render_body)
+}
+
+/// The gain module with its own manifest JSON.
+fn module_with(manifest: &str, render_body: &str) -> String {
     let len = manifest.len();
     let escaped = manifest.replace('\\', "\\\\").replace('"', "\\\"");
     format!(
@@ -162,3 +171,149 @@ fn wasm_plugins_are_sandboxed() {
     let reserved = gain_module("ec.blur.mine", "");
     assert!(load_err(load_wasm(reserved.as_bytes(), "reserved.wat")).contains("reserved"));
 }
+
+/// `base` with `from` replaced by `to` (which must occur).
+fn edit(base: &str, from: &str, to: &str) -> String {
+    assert!(base.contains(from), "{from}");
+    base.replace(from, to)
+}
+
+#[test]
+fn abi_violations_fail_to_load_with_reasons() {
+    let base = gain_module("org.test.abi", "");
+    // Missing exports.
+    for export in ["ec_render", "ec_alloc", "ec_manifest_ptr", "ec_manifest_len", "ec_api_version"] {
+        let m = edit(&base, &format!("(export \"{export}\")"), "");
+        let e = load_err(load_wasm(m.as_bytes(), "x.wat"));
+        assert!(e.contains(export), "{export}: {e}");
+    }
+    let m = edit(&base, "(memory (export \"memory\") 2)", "(memory 2)");
+    assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains("memory"));
+    // Wrong signatures.
+    let m = edit(&base, "(func (export \"ec_api_version\") (result i32) i32.const 1)", "(func (export \"ec_api_version\") (result f64) f64.const 1)");
+    assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains("ec_api_version"));
+    let m = edit(&base, "(param $scale f64) (result i32)", "(param $scale f32) (result i32)");
+    assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains("ec_render"));
+    // API versions other than 1.
+    for v in ["0", "-1", "2147483647"] {
+        let m = edit(
+            &base,
+            "(func (export \"ec_api_version\") (result i32) i32.const 1)",
+            &format!("(func (export \"ec_api_version\") (result i32) i32.const {v})"),
+        );
+        assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains(&format!("API {v}")), "{v}");
+    }
+    // Manifest out of bounds, negative or absurd lengths, not JSON.
+    let ptr = "(func (export \"ec_manifest_ptr\") (result i32) i32.const 16)";
+    let m = edit(&base, ptr, "(func (export \"ec_manifest_ptr\") (result i32) i32.const 200000)");
+    assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains("out of bounds"));
+    let len = gain_manifest("org.test.abi").len();
+    for bad in ["-5", "2000000000"] {
+        let m = edit(&base, &format!("(result i32) i32.const {len})"), &format!("(result i32) i32.const {bad})"));
+        assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains("manifest length"), "{bad}");
+    }
+    let m = edit(&base, ptr, "(func (export \"ec_manifest_ptr\") (result i32) i32.const 4000)");
+    assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains("manifest JSON"));
+    // Traps and runaway code while loading.
+    let version = "(func (export \"ec_api_version\") (result i32) i32.const 1)";
+    let m = edit(&base, version, "(func (export \"ec_api_version\") (result i32) unreachable)");
+    assert!(load_wasm(m.as_bytes(), "x.wat").is_err());
+    let m = edit(&base, version, "(func (export \"ec_api_version\") (result i32) (loop $l br $l) i32.const 1)");
+    assert!(load_wasm(m.as_bytes(), "x.wat").is_err(), "fuel runs out in ec_api_version");
+    let m = edit(&base, "(memory (export \"memory\") 2)", "(memory (export \"memory\") 2) (func $s (loop $l br $l)) (start $s)");
+    assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains("instantiation"), "fuel runs out in the start function");
+    // Memory beyond the sandbox's limit.
+    let m = edit(&base, "(memory (export \"memory\") 2)", "(memory (export \"memory\") 20000)");
+    assert!(load_err(load_wasm(m.as_bytes(), "x.wat")).contains("instantiation"));
+    // Not a module at all.
+    for junk in [&b""[..], b"\0asm", b"\0asm\x01\0\0\0\xff\xff", b"(module", b"(module (func (export \"x\") unknown_op))"] {
+        assert!(load_wasm(junk, "junk").is_err());
+    }
+}
+
+#[test]
+fn manifest_parameter_schemas_are_validated() {
+    let p = |params: &str| format!(r#"{{"api":1,"id":"org.test.schema","name":"Schema","category":"Test Plug-ins","version":"1","params":[{params}]}}"#);
+    let bad = [
+        (r#"{"id":"a","name":"A","type":"checkbox"},{"id":"a","name":"B","type":"checkbox"}"#, "duplicate"),
+        (r#"{"id":"a b","name":"A","type":"checkbox"}"#, "parameter id"),
+        (r#"{"id":"","name":"A","type":"checkbox"}"#, "parameter id"),
+        (r#"{"id":"p","name":"P","type":"popup","options":[],"default":0}"#, "popup"),
+        (r#"{"id":"p","name":"P","type":"popup","options":["x"],"default":3}"#, "popup"),
+        (r#"{"id":"s","name":"S","type":"slider","default":1,"min":5,"max":0}"#, "slider"),
+        (r#"{"id":"s","name":"S","type":"slider","default":9,"min":0,"max":4}"#, "slider"),
+        (r#"{"id":"s","name":"S","type":"slider","default":1,"min":0,"max":4,"sliderMin":3,"sliderMax":2}"#, "slider"),
+        (r#"{"id":"s","name":"S","type":"wobble"}"#, "manifest JSON"),
+        (r#"{"id":"s","name":"S","type":"slider"}"#, "manifest JSON"),
+    ];
+    for (params, want) in bad {
+        let m = module_with(&p(params), "");
+        let e = load_err(load_wasm(m.as_bytes(), "schema.wat"));
+        assert!(e.contains(want), "{params}: {e}");
+    }
+    let many: Vec<String> = (0..300).map(|i| format!(r#"{{"id":"c{i}","name":"C","type":"checkbox"}}"#)).collect();
+    let e = load_err(load_wasm(module_with(&p(&many.join(",")), "").as_bytes(), "many.wat"));
+    assert!(e.contains("at most"), "{e}");
+    // Missing name, another API in the manifest.
+    let e = load_err(load_wasm(module_with(r#"{"api":1,"id":"org.test.noname","name":" ","category":"X","version":"1","params":[]}"#, "").as_bytes(), "x.wat"));
+    assert!(e.contains("name"), "{e}");
+    let e = load_err(load_wasm(module_with(r#"{"api":3,"id":"org.test.api3","name":"N","category":"X","version":"1","params":[]}"#, "").as_bytes(), "x.wat"));
+    assert!(e.contains("API 3"), "{e}");
+    // A valid schema loads.
+    let ok = p(
+        r#"{"id":"s","name":"S","type":"slider","default":2,"min":0,"max":4,"sliderMin":1,"sliderMax":3},{"id":"p","name":"P","type":"popup","options":["x","y"],"default":1}"#,
+    );
+    let spec = load_wasm(module_with(&ok, "").as_bytes(), "ok.wat").unwrap();
+    assert_eq!(spec.params.len(), 2);
+}
+
+#[test]
+fn render_failures_leave_the_frame_and_recover() {
+    let orig = [0.8, 0.6, 0.2, 1.0];
+    // ec_render traps (when time > 0.5), returns an error code, or ec_alloc hands back memory
+    // out of bounds: the frame passes through unchanged, and the plug-in keeps working.
+    let trap = load_wasm(gain_module("org.test.trap", "local.get $t f64.const 0.5 f64.gt if unreachable end").as_bytes(), "trap.wat").unwrap();
+    let mut next = 1;
+    let g = effectcraft_effects::instantiate(trap, &mut Ids(&mut next), trap.name, [4.0, 2.0]);
+    let params = effectcraft_effects::flatten_params(&g, &mut |p| p.value.clone());
+    let at = |time: f64| {
+        let ctx = EffectCtx { params: &params, time, layer_size: [4.0, 2.0], seed: 1, adjustment: false, env: EffectEnv::default() };
+        let buf = Buf { img: Image::filled(4, 2, orig), offset: [0.0; 2], scale: 1.0 };
+        (trap.render)(&ctx, buf).img
+    };
+    assert_eq!(at(1.0).get(0, 0), orig, "trapped");
+    assert_eq!(at(0.0).get(0, 0), [0.4, 0.3, 0.1, 1.0], "a fresh instance after the trap");
+    assert_eq!(at(1.0).get(0, 0), orig);
+    assert_eq!(at(0.0).get(1, 1), [0.4, 0.3, 0.1, 1.0]);
+    let code = load_wasm(gain_module("org.test.code", "i32.const 7 return").as_bytes(), "code.wat").unwrap();
+    assert_eq!(render(code, 0.5, false).get(0, 0), orig);
+    let oob = edit(&gain_module("org.test.oob", ""), "    i32.const 65536)", "    i32.const -16)");
+    let oob = load_wasm(oob.as_bytes(), "oob.wat").unwrap();
+    assert_eq!(render(oob, 0.5, false).get(0, 0), orig);
+    // Runaway rendering: out of fuel every time, never hangs.
+    let spin = load_wasm(gain_module("org.test.spin2", "(loop $spin br $spin)").as_bytes(), "spin2.wat").unwrap();
+    for _ in 0..3 {
+        assert_eq!(render(spin, 0.5, false).get(0, 0), orig);
+    }
+}
+
+#[test]
+fn wasm_rendering_is_deterministic() {
+    // Float edge cases (NaN from sqrt(−x), infinities from x / 0) come out bit-identical
+    // across instances, threads and repeated runs.
+    let body = "local.get $px local.get $px f32.load f32.const -1 f32.mul f32.sqrt f32.store \
+                local.get $px local.get $px f32.load offset=4 f32.const 0 f32.div f32.store offset=4";
+    let spec = load_wasm(gain_module("org.test.det", body).as_bytes(), "det.wat").unwrap();
+    let bits = |img: &Image| -> Vec<u32> { (0..2).flat_map(|y| (0..4).map(move |x| (x, y))).flat_map(|(x, y)| img.get(x, y).map(f32::to_bits)).collect() };
+    let first = bits(&render(spec, 0.37, true));
+    let runs: Vec<Vec<u32>> = std::thread::scope(|sc| {
+        let hs: Vec<_> = (0..6).map(|_| sc.spawn(|| bits(&render(spec, 0.37, true)))).collect();
+        hs.into_iter().map(|h| h.join().unwrap()).collect()
+    });
+    for r in runs {
+        assert_eq!(r, first);
+    }
+    // The same module loaded under another id renders the same bits.
+    let twin = load_wasm(gain_module("org.test.det2", body).as_bytes(), "det2.wat").unwrap();
+    assert_eq!(bits(&render(twin, 0.37, true)), first);
+}
diff --git a/crates/plugin/src/wasm.rs b/crates/plugin/src/wasm.rs
index 8015f7ee..71f1f136 100644
--- a/crates/plugin/src/wasm.rs
+++ b/crates/plugin/src/wasm.rs
@@ -2,7 +2,7 @@
 
 use std::sync::Mutex;
 
-use wasmi::{Config, Engine, Instance, Linker, Memory, Module, Store, TypedFunc, WasmParams, WasmResults};
+use wasmi::{Config, Engine, Instance, Linker, Memory, Module, Store, StoreLimits, StoreLimitsBuilder, TypedFunc, WasmParams, WasmResults};
 
 use crate::{EffectPlugin, PLUGIN_API_VERSION, PluginFrame, PluginManifest, PluginParams};
 
@@ -10,12 +10,16 @@ use crate::{EffectPlugin, PLUGIN_API_VERSION, PluginFrame, PluginManifest, Plugi
 /// work, but a runaway loop stops instead of hanging the render.
 const FUEL_BASE: u64 = 50_000_000;
 const FUEL_PER_PIXEL: u64 = 20_000;
+/// The most linear memory a plug-in instance may have (a 4K float frame is ~130 MB).
+const MAX_MEMORY: usize = 1 << 30;
+/// The longest manifest read.
+const MAX_MANIFEST: i32 = 1 << 20;
 
 type RenderFn = TypedFunc<(i32, i32, i32, i32, i32, f64, f64), i32>;
 
 /// One instantiated module (renders running on several threads each take their own).
 struct Inst {
-    store: Store<()>,
+    store: Store<StoreLimits>,
     instance: Instance,
     memory: Memory,
     alloc: TypedFunc<i32, i32>,
@@ -37,9 +41,10 @@ fn err(e: impl std::fmt::Display) -> String {
 }
 
 fn instantiate(engine: &Engine, module: &Module) -> Result<Inst, String> {
-    let mut store = Store::new(engine, ());
+    let mut store = Store::new(engine, StoreLimitsBuilder::new().memory_size(MAX_MEMORY).instances(1).build());
+    store.limiter(|l| l);
     store.set_fuel(FUEL_BASE).map_err(err)?;
-    let linker = Linker::<()>::new(engine);
+    let linker = Linker::<StoreLimits>::new(engine);
     let instance = linker.instantiate_and_start(&mut store, module).map_err(|e| format!("instantiation failed: {e}"))?;
     let memory = instance.get_memory(&store, "memory").ok_or("the module exports no `memory`")?;
     let alloc = instance.get_typed_func::<i32, i32>(&store, "ec_alloc").map_err(|_| missing("ec_alloc"))?;
@@ -74,7 +79,10 @@ impl WasmPlugin {
         }
         let ptr = inst.func::<(), i32>("ec_manifest_ptr")?.call(&mut inst.store, ()).map_err(err)?;
         let len = inst.func::<(), i32>("ec_manifest_len")?.call(&mut inst.store, ()).map_err(err)?;
-        let mut text = vec![0u8; len.max(0) as usize];
+        if !(0..=MAX_MANIFEST).contains(&len) {
+            return Err(format!("bad manifest length {len}"));
+        }
+        let mut text = vec![0u8; len as usize];
         inst.memory.read(&inst.store, ptr as u32 as usize, &mut text).map_err(|e| format!("manifest out of bounds: {e}"))?;
         let manifest: PluginManifest = serde_json::from_slice(&text).map_err(|e| format!("bad manifest JSON: {e}"))?;
         manifest.validate()?;