diff --git a/crates/config-source-wasm/src/lib.rs b/crates/config-source-wasm/src/lib.rs
index f15c6f7b..6df1e834 100644
--- a/crates/config-source-wasm/src/lib.rs
+++ b/crates/config-source-wasm/src/lib.rs
@@ -8,6 +8,7 @@ use wasm_bindgen::prelude::*;
 
 thread_local! {
     static SESSION: RefCell<Option<ConfigTreeSnapshot>> = const { RefCell::new(None) };
+    static SCHEMA_BUNDLE: RefCell<Option<WorkspaceConfigSchemaBundle>> = const { RefCell::new(None) };
 }
 
 #[wasm_bindgen]
@@ -23,6 +24,13 @@ pub fn set_snapshot(snapshot: JsValue) -> Result<(), JsValue> {
     Ok(())
 }
 
+#[wasm_bindgen]
+pub fn set_schema_bundle(schema_bundle: JsValue) -> Result<(), JsValue> {
+    let schema_bundle: WorkspaceConfigSchemaBundle = decode(schema_bundle)?;
+    SCHEMA_BUNDLE.with(|session| session.replace(Some(schema_bundle)));
+    Ok(())
+}
+
 #[wasm_bindgen]
 pub fn apply_changes(changes: JsValue) -> Result<JsValue, JsValue> {
     let changes: Vec<ConfigTreeChange> = decode(changes)?;
@@ -91,8 +99,8 @@ pub fn complete_current(
             .as_ref()
             .ok_or_else(|| JsValue::from_str("config source snapshot is not initialized"))?;
         let utf8_byte_offset = utf16_to_utf8_offset(&source, utf16_offset)?;
-        let result = SnapshotEnvironment::new(snapshot.clone())
-            .complete(&entrypoint, &source, utf8_byte_offset, explicit)
+        let result = session_environment(snapshot.clone())
+            .complete_config(&entrypoint, &source, utf8_byte_offset, explicit)
             .map_err(|error| JsValue::from_str(&format!("{error:?}")))?
             .map(|result| WasmCompletionResult {
                 from: result.from,
@@ -132,7 +140,16 @@ pub fn analyze_snapshot(
 ) -> Result<JsValue, JsValue> {
     let snapshot: ConfigTreeSnapshot = decode(snapshot)?;
     let entrypoint = VirtualPath::parse(entrypoint).map_err(js_error)?;
-    encode(SnapshotEnvironment::new(snapshot).analyze(&entrypoint, source_override.as_deref()))
+    encode(session_environment(snapshot).analyze(&entrypoint, source_override.as_deref()))
+}
+
+fn session_environment(snapshot: ConfigTreeSnapshot) -> SnapshotEnvironment {
+    let schema_bundle = SCHEMA_BUNDLE.with(|schema_bundle| schema_bundle.borrow().clone());
+    let mut environment = SnapshotEnvironment::new(snapshot);
+    if let Some(schema_bundle) = schema_bundle {
+        environment = environment.with_schema_bundle(schema_bundle);
+    }
+    environment
 }
 
 #[wasm_bindgen]
diff --git a/crates/config-source/src/lib.rs b/crates/config-source/src/lib.rs
index 1dd92cc5..2219973b 100644
--- a/crates/config-source/src/lib.rs
+++ b/crates/config-source/src/lib.rs
@@ -3,7 +3,7 @@ use std::fmt;
 
 use decodal::{
     Data, Diagnostic, DiagnosticKind, Engine, HostEnvironment, ImportCandidate, ImportLoader,
-    LoadedImport, Span, Value,
+    LoadedImport, Span, SyntaxToken, SyntaxTokenKind, Value, tokenize_source,
 };
 use decodal_language_service::{CompletionResult, LanguageService};
 use serde::{Deserialize, Serialize};
@@ -752,14 +752,249 @@ pub struct EvaluationResult {
     pub projection_digest: String,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct ConfigFieldCompletionContext {
+    schema_path: Vec<String>,
+    from: usize,
+}
+
+#[derive(Debug)]
+enum ConfigCompletionContainer {
+    Object {
+        schema_path: Vec<String>,
+        pending_path: Vec<String>,
+        last_identifier_from: Option<usize>,
+        trailing_dot: bool,
+        reading_value: bool,
+    },
+    Array {
+        schema_path: Vec<String>,
+    },
+    Other {
+        schema_path: Vec<String>,
+    },
+}
+
+fn workspace_schema_assertion_object_start(
+    tokens: &[SyntaxToken],
+    utf8_byte_offset: usize,
+) -> Option<usize> {
+    let mut object_stack = Vec::<usize>::new();
+    let mut matching_assertions = Vec::<usize>::new();
+
+    for (index, token) in tokens.iter().enumerate() {
+        match &token.kind {
+            SyntaxTokenKind::LBrace => object_stack.push(index),
+            SyntaxTokenKind::RBrace => {
+                let Some(object_index) = object_stack.pop() else {
+                    continue;
+                };
+                let object_start = tokens[object_index].span.start as usize;
+                let object_end = token.span.start as usize;
+                if !(object_start < utf8_byte_offset && utf8_byte_offset <= object_end) {
+                    continue;
+                }
+                let mut suffix = tokens[index + 1..]
+                    .iter()
+                    .filter(|token| !matches!(token.kind, SyntaxTokenKind::Comment));
+                if !matches!(
+                    suffix.next().map(|token| &token.kind),
+                    Some(SyntaxTokenKind::As)
+                ) {
+                    continue;
+                }
+                let Some(SyntaxTokenKind::Ident(global)) = suffix.next().map(|token| &token.kind)
+                else {
+                    continue;
+                };
+                if global == WORKSPACE_CONFIG_SCHEMA_GLOBAL {
+                    matching_assertions.push(object_start);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    matching_assertions.into_iter().max()
+}
+
+fn config_field_completion_context(
+    source: &str,
+    utf8_byte_offset: usize,
+) -> Option<ConfigFieldCompletionContext> {
+    if utf8_byte_offset > source.len() || !source.is_char_boundary(utf8_byte_offset) {
+        return None;
+    }
+    let tokens = tokenize_source(source).ok()?;
+    let asserted_object_start = workspace_schema_assertion_object_start(&tokens, utf8_byte_offset)?;
+    let mut containers = Vec::<ConfigCompletionContainer>::new();
+
+    for token in tokens {
+        let token_start = token.span.start as usize;
+        let token_end = token.span.end as usize;
+        if token_start < asserted_object_start {
+            continue;
+        }
+        if token_start >= utf8_byte_offset {
+            break;
+        }
+        let kind = token.kind;
+        match kind {
+            SyntaxTokenKind::LBrace => {
+                let schema_path = pending_container_path(&containers);
+                containers.push(ConfigCompletionContainer::Object {
+                    schema_path,
+                    pending_path: Vec::new(),
+                    last_identifier_from: None,
+                    trailing_dot: false,
+                    reading_value: false,
+                });
+            }
+            SyntaxTokenKind::RBrace => {
+                pop_container(&mut containers, |container| {
+                    matches!(container, ConfigCompletionContainer::Object { .. })
+                });
+            }
+            SyntaxTokenKind::LBracket => {
+                let schema_path = pending_container_path(&containers);
+                containers.push(ConfigCompletionContainer::Array { schema_path });
+            }
+            SyntaxTokenKind::RBracket => {
+                pop_container(&mut containers, |container| {
+                    matches!(container, ConfigCompletionContainer::Array { .. })
+                });
+            }
+            SyntaxTokenKind::LParen => {
+                let schema_path = pending_container_path(&containers);
+                containers.push(ConfigCompletionContainer::Other { schema_path });
+            }
+            SyntaxTokenKind::RParen => {
+                pop_container(&mut containers, |container| {
+                    matches!(container, ConfigCompletionContainer::Other { .. })
+                });
+            }
+            SyntaxTokenKind::Ident(identifier) => {
+                let Some(ConfigCompletionContainer::Object {
+                    pending_path,
+                    last_identifier_from,
+                    trailing_dot,
+                    reading_value: false,
+                    ..
+                }) = containers.last_mut()
+                else {
+                    continue;
+                };
+                let identifier = if token_end > utf8_byte_offset {
+                    source[token_start..utf8_byte_offset].to_owned()
+                } else {
+                    identifier
+                };
+                if *trailing_dot || pending_path.is_empty() {
+                    pending_path.push(identifier);
+                } else {
+                    *pending_path.last_mut().expect("pending path is non-empty") = identifier;
+                }
+                *last_identifier_from = Some(token_start);
+                *trailing_dot = false;
+            }
+            SyntaxTokenKind::Dot => {
+                if let Some(ConfigCompletionContainer::Object {
+                    trailing_dot,
+                    reading_value: false,
+                    ..
+                }) = containers.last_mut()
+                {
+                    *trailing_dot = true;
+                }
+            }
+            SyntaxTokenKind::Equal => {
+                if let Some(ConfigCompletionContainer::Object { reading_value, .. }) =
+                    containers.last_mut()
+                {
+                    *reading_value = true;
+                }
+            }
+            SyntaxTokenKind::Semicolon => {
+                if let Some(ConfigCompletionContainer::Object {
+                    pending_path,
+                    last_identifier_from,
+                    trailing_dot,
+                    reading_value,
+                    ..
+                }) = containers.last_mut()
+                {
+                    pending_path.clear();
+                    *last_identifier_from = None;
+                    *trailing_dot = false;
+                    *reading_value = false;
+                }
+            }
+            _ => {}
+        }
+    }
+
+    let ConfigCompletionContainer::Object {
+        schema_path,
+        pending_path,
+        last_identifier_from,
+        trailing_dot,
+        reading_value: false,
+    } = containers.last()?
+    else {
+        return None;
+    };
+    let mut schema_path = schema_path.clone();
+    schema_path.extend(pending_path.iter().cloned());
+    Some(ConfigFieldCompletionContext {
+        schema_path,
+        from: if *trailing_dot {
+            utf8_byte_offset
+        } else {
+            last_identifier_from.unwrap_or(utf8_byte_offset)
+        },
+    })
+}
+
+fn pending_container_path(containers: &[ConfigCompletionContainer]) -> Vec<String> {
+    match containers.last() {
+        Some(ConfigCompletionContainer::Object {
+            schema_path,
+            pending_path,
+            reading_value: true,
+            ..
+        }) => schema_path.iter().chain(pending_path).cloned().collect(),
+        Some(ConfigCompletionContainer::Array { schema_path })
+        | Some(ConfigCompletionContainer::Other { schema_path }) => schema_path.clone(),
+        _ => Vec::new(),
+    }
+}
+
+fn pop_container(
+    containers: &mut Vec<ConfigCompletionContainer>,
+    matches: impl Fn(&ConfigCompletionContainer) -> bool,
+) {
+    if let Some(index) = containers.iter().rposition(matches) {
+        containers.truncate(index);
+    }
+}
+
 #[derive(Debug, Clone)]
 pub struct SnapshotEnvironment {
     snapshot: ConfigTreeSnapshot,
+    schema_bundle: Option<WorkspaceConfigSchemaBundle>,
 }
 
 impl SnapshotEnvironment {
     pub fn new(snapshot: ConfigTreeSnapshot) -> Self {
-        Self { snapshot }
+        Self {
+            snapshot,
+            schema_bundle: None,
+        }
+    }
+
+    pub fn with_schema_bundle(mut self, schema_bundle: WorkspaceConfigSchemaBundle) -> Self {
+        self.schema_bundle = Some(schema_bundle);
+        self
     }
 
     pub fn snapshot(&self) -> &ConfigTreeSnapshot {
@@ -954,6 +1189,32 @@ impl SnapshotEnvironment {
         LanguageService::new(self).complete(entrypoint.as_str(), source, utf8_byte_offset, explicit)
     }
 
+    pub fn complete_config(
+        &self,
+        entrypoint: &VirtualPath,
+        source: &str,
+        utf8_byte_offset: usize,
+        explicit: bool,
+    ) -> decodal::Result<Option<CompletionResult>> {
+        if self.schema_bundle.is_some()
+            && let Some(context) = config_field_completion_context(source, utf8_byte_offset)
+        {
+            let mut member_source = format!("{WORKSPACE_CONFIG_SCHEMA_GLOBAL}.");
+            member_source.push_str(&context.schema_path.join("."));
+            let mut completion = LanguageService::new(self).complete(
+                entrypoint.as_str(),
+                &member_source,
+                member_source.len(),
+                explicit,
+            )?;
+            if let Some(completion) = &mut completion {
+                completion.from = context.from;
+            }
+            return Ok(completion);
+        }
+        self.complete(entrypoint, source, utf8_byte_offset, explicit)
+    }
+
     pub fn format(&self, source: &str) -> Result<String, String> {
         decodal_language_tools::format_source(source).map_err(|error| error.to_string())
     }
@@ -989,7 +1250,17 @@ impl HostEnvironment for &SnapshotEnvironment {
         }
     }
 
-    fn configure_engine(&self, _engine: &mut Engine<Self::Loader>) -> decodal::Result<()> {
+    fn configure_engine(&self, engine: &mut Engine<Self::Loader>) -> decodal::Result<()> {
+        let Some(schema_bundle) = &self.schema_bundle else {
+            return Ok(());
+        };
+        let schema_module = engine.add_root_source(
+            WORKSPACE_CONFIG_SCHEMA_SOURCE,
+            WORKSPACE_CONFIG_SCHEMA_SOURCE,
+            &schema_bundle.source,
+        )?;
+        let schema = engine.eval_module(schema_module)?;
+        engine.bind_global_runtime(WORKSPACE_CONFIG_SCHEMA_GLOBAL, schema);
         Ok(())
     }
 }
@@ -1576,6 +1847,91 @@ mod tests {
         assert_eq!(left.digest, right.digest);
     }
 
+    #[test]
+    fn schema_completion_tracks_only_asserted_config_object_paths() {
+        assert_eq!(config_field_completion_context("{ pro", 5), None);
+
+        let root = "{ pro } as WorkspaceConfigSchema";
+        let root_cursor = root.find("pro").unwrap() + 3;
+        assert_eq!(
+            config_field_completion_context(root, root_cursor),
+            Some(ConfigFieldCompletionContext {
+                schema_path: vec!["pro".into()],
+                from: root_cursor - 3,
+            })
+        );
+        let nested = "{ profile = { def } } as WorkspaceConfigSchema";
+        let nested_cursor = nested.find("def").unwrap() + 3;
+        assert_eq!(
+            config_field_completion_context(nested, nested_cursor),
+            Some(ConfigFieldCompletionContext {
+                schema_path: vec!["profile".into(), "def".into()],
+                from: nested_cursor - 3,
+            })
+        );
+        let array = "{ profile = { entries = [{ sel }] } } as WorkspaceConfigSchema";
+        let array_cursor = array.find("sel").unwrap() + 3;
+        assert_eq!(
+            config_field_completion_context(array, array_cursor),
+            Some(ConfigFieldCompletionContext {
+                schema_path: vec!["profile".into(), "entries".into(), "sel".into()],
+                from: array_cursor - 3,
+            })
+        );
+        let value = "{ profile = \"default\" } as WorkspaceConfigSchema";
+        let value_cursor = value.find("default").unwrap() + 3;
+        assert_eq!(config_field_completion_context(value, value_cursor), None);
+    }
+
+    #[test]
+    fn completion_projects_workspace_schema_fields_into_config_objects() {
+        let snapshot = ConfigTreeSnapshot::from_entries(1, [entry("main.dcdl", "{}")]).unwrap();
+        let schema = WorkspaceConfigSchemaBundle::compose([ConfigSchemaContribution::new(
+            "builtin:profile",
+            "profile",
+            "1",
+            "{ profile = { default_profile = String; entries = [{ selector = String; }]; }; }",
+        )
+        .unwrap()])
+        .unwrap();
+        let environment = SnapshotEnvironment::new(snapshot).with_schema_bundle(schema);
+
+        let bare_source = "{ pro }";
+        let bare_cursor = bare_source.find("pro").unwrap() + 3;
+        let bare = environment
+            .complete_config(&path("main.dcdl"), bare_source, bare_cursor, true)
+            .unwrap();
+        assert!(
+            bare.is_none_or(|completion| !completion
+                .items
+                .iter()
+                .any(|item| item.label == "profile"))
+        );
+
+        let root_source = "{ pro } as WorkspaceConfigSchema";
+        let root_cursor = root_source.find("pro").unwrap() + 3;
+        let root = environment
+            .complete_config(&path("main.dcdl"), root_source, root_cursor, true)
+            .unwrap()
+            .unwrap();
+        assert_eq!(root.from, root_cursor - 3);
+        assert!(root.items.iter().any(|item| item.label == "profile"));
+
+        let nested_source = "{ profile = { def } } as WorkspaceConfigSchema";
+        let nested_cursor = nested_source.find("def").unwrap() + 3;
+        let nested = environment
+            .complete_config(&path("main.dcdl"), nested_source, nested_cursor, true)
+            .unwrap()
+            .unwrap();
+        assert_eq!(nested.from, nested_cursor - 3);
+        assert!(
+            nested
+                .items
+                .iter()
+                .any(|item| item.label == "default_profile")
+        );
+    }
+
     #[test]
     fn relative_imports_and_completion_share_the_snapshot_namespace() {
         let snapshot = ConfigTreeSnapshot::from_entries(
diff --git a/web/workspace/deno.json b/web/workspace/deno.json
index a86241c8..06f4bf98 100644
--- a/web/workspace/deno.json
+++ b/web/workspace/deno.json
@@ -6,7 +6,7 @@
     "dev": "deno run -A npm:vite@7.2.7 dev",
     "dev:backend": "cd ../.. && cargo run -p yoi-workspace-server --bin yoi-server -- serve --listen 127.0.0.1:8787",
     "check": "deno run -A npm:@sveltejs/kit@2.49.4 sync && deno run -A npm:svelte-check@4.3.4 --tsconfig ./tsconfig.json",
-    "test": "deno test --allow-read=src,test --allow-env=LOG,VSCODE_TEXTMATE_DEBUG src/lib/workspace/auth/model.test.ts src/lib/workspace/api/http.test.ts src/lib/workspace/header/breadcrumb-model.test.ts src/lib/workspace/console/chat-submit.test.ts src/lib/workspace/console/composer-command.test.ts src/lib/workspace/console/composer-completion.test.ts src/lib/workspace/console/markdown.test.ts src/lib/workspace/console/model.test.ts src/lib/workspace/console/tasks.test.ts src/lib/workspace/console/worker-console.ui.test.ts src/lib/workspace/settings/model.test.ts src/lib/workspace/sidebar/workers.test.ts src/lib/workspace/sidebar/worker-subscription.test.ts src/lib/workspace/sidebar/worker-launch.test.ts src/lib/workspace/sidebar/repository-nav.test.ts src/lib/workspace/tickets/ticket-panel.test.ts test/config-source/decodal-grammar.test.ts test/config-source/wasm-parity.test.ts",
+    "test": "deno test --allow-read=src,test --allow-env=LOG,VSCODE_TEXTMATE_DEBUG src/lib/workspace/auth/model.test.ts src/lib/workspace/api/http.test.ts src/lib/workspace/header/breadcrumb-model.test.ts src/lib/workspace/console/chat-submit.test.ts src/lib/workspace/console/composer-command.test.ts src/lib/workspace/console/composer-completion.test.ts src/lib/workspace/console/markdown.test.ts src/lib/workspace/console/model.test.ts src/lib/workspace/console/tasks.test.ts src/lib/workspace/console/worker-console.ui.test.ts src/lib/workspace/settings/model.test.ts src/lib/workspace/sidebar/workers.test.ts src/lib/workspace/sidebar/worker-subscription.test.ts src/lib/workspace/sidebar/worker-launch.test.ts src/lib/workspace/sidebar/repository-nav.test.ts src/lib/workspace/tickets/ticket-panel.test.ts test/config-source/decodal-grammar.test.ts test/config-source/editor-state.test.ts test/config-source/toolchain.test.ts test/config-source/wasm-parity.test.ts",
     "build": "deno run -A npm:vite@7.2.7 build",
     "preview": "deno run -A npm:vite@7.2.7 preview"
   },
@@ -16,8 +16,10 @@
     "@sveltejs/kit": "npm:@sveltejs/kit@2.49.4",
     "@sveltejs/vite-plugin-svelte": "npm:@sveltejs/vite-plugin-svelte@6.2.1",
     "@codemirror/autocomplete": "npm:@codemirror/autocomplete@6.20.0",
+    "@codemirror/language": "npm:@codemirror/language@6.12.4",
     "@codemirror/state": "npm:@codemirror/state@6.7.1",
     "@codemirror/view": "npm:@codemirror/view@6.43.8",
+    "@lezer/highlight": "npm:@lezer/highlight@1.2.3",
     "decodal-codemirror": "npm:decodal-codemirror@0.3.0",
     "clsx": "npm:clsx@2.1.1",
     "cookie": "npm:cookie@0.6.0",
diff --git a/web/workspace/deno.lock b/web/workspace/deno.lock
index d25f484e..a68fd449 100644
--- a/web/workspace/deno.lock
+++ b/web/workspace/deno.lock
@@ -4,9 +4,11 @@
     "jsr:@std/assert@*": "1.0.19",
     "jsr:@std/internal@^1.0.12": "1.0.14",
     "npm:@codemirror/autocomplete@6.20.0": "6.20.0",
+    "npm:@codemirror/language@6.12.4": "6.12.4",
     "npm:@codemirror/state@6.7.1": "6.7.1",
     "npm:@codemirror/view@6.43.8": "6.43.8",
     "npm:@fontsource/ibm-plex-mono@5.3.0": "5.3.0",
+    "npm:@lezer/highlight@1.2.3": "1.2.3",
     "npm:@sveltejs/adapter-static@3.0.9": "3.0.9_@sveltejs+kit@2.49.4__@sveltejs+vite-plugin-svelte@6.2.1___svelte@5.45.6___vite@7.2.7__svelte@5.45.6__typescript@5.9.3__vite@7.2.7_@sveltejs+vite-plugin-svelte@6.2.1__svelte@5.45.6__vite@7.2.7_svelte@5.45.6_typescript@5.9.3_vite@7.2.7",
     "npm:@sveltejs/kit@2.49.4": "2.49.4_@sveltejs+vite-plugin-svelte@6.2.1__svelte@5.45.6__vite@7.2.7_svelte@5.45.6_typescript@5.9.3_vite@7.2.7",
     "npm:@sveltejs/vite-plugin-svelte@6.2.1": "6.2.1_svelte@5.45.6_vite@7.2.7",
@@ -509,7 +511,8 @@
       "integrity": "sha512-/iZM6FnM4tnx9csuTxspMW4BOSegshwX5oBDznJ7S4WggL7Vczz5d2W11ecc4vRrQMQHXRSxzrCsyG5EsPPTbA=="
     },
     "@ungap/structured-clone@1.3.0": {
-      "integrity": "sha512-WmoN8qaIAo7WTYWbAZuG8PYEhn5fkz7dZrqTBZ7dtt//lL2Gwms1IcnQ5yHqjDfX8Ft5j4YzDM23f87zBfDe9g=="
+      "integrity": "sha512-WmoN8qaIAo7WTYWbAZuG8PYEhn5fkz7dZrqTBZ7dtt//lL2Gwms1IcnQ5yHqjDfX8Ft5j4YzDM23f87zBfDe9g==",
+      "deprecated": true
     },
     "acorn@8.16.0": {
       "integrity": "sha512-UVJyE9MttOsBQIDKw1skb9nAwQuR5wuGD3+82K6JgJlm/Y+KI92oNsMNGZCYdDsVtRHSak0pcV5Dno5+4jh9sw==",
@@ -1000,8 +1003,10 @@
   "workspace": {
     "dependencies": [
       "npm:@codemirror/autocomplete@6.20.0",
+      "npm:@codemirror/language@6.12.4",
       "npm:@codemirror/state@6.7.1",
       "npm:@codemirror/view@6.43.8",
+      "npm:@lezer/highlight@1.2.3",
       "npm:@sveltejs/adapter-static@3.0.9",
       "npm:@sveltejs/kit@2.49.4",
       "npm:@sveltejs/vite-plugin-svelte@6.2.1",
diff --git a/web/workspace/src/lib/workspace/config-source/ConfigSourceEditor.svelte b/web/workspace/src/lib/workspace/config-source/ConfigSourceEditor.svelte
index b6303733..cfb9142b 100644
--- a/web/workspace/src/lib/workspace/config-source/ConfigSourceEditor.svelte
+++ b/web/workspace/src/lib/workspace/config-source/ConfigSourceEditor.svelte
@@ -27,7 +27,7 @@
   let baseRevision = $state(0);
   let baseDigest = $state("");
   let renamePath = $state("");
-  let baseSnapshot = $state<WorkspaceConfigTreeResponse["snapshot"] | null>(null);
+  let baseSnapshot = $state.raw<WorkspaceConfigTreeResponse["snapshot"] | null>(null);
   let preflightDigest = $state("");
   let conflict = $state(false);
   let candidateContract = $state<WorkspaceConfigTreeResponse["contract"] | null>(null);
@@ -56,10 +56,10 @@
         selectedPath = Object.keys(treeState.snapshot.entries).toSorted()[0] ?? "";
       }
       source = selectedPath ? treeState.snapshot.entries[selectedPath].content : "";
-      baseSnapshot = structuredClone(treeState.snapshot);
+      baseSnapshot = $state.snapshot(treeState.snapshot);
       baseRevision = treeState.snapshot.revision;
       baseDigest = treeState.snapshot.digest;
-      await toolchain?.setSnapshot(treeState.snapshot);
+      await toolchain?.setSnapshot(treeState.snapshot, treeState.contract.schema_bundle);
       draftChanges = [];
       renamePath = selectedPath;
       diagnostics = [];
@@ -181,10 +181,10 @@
       preflightDigest = "";
     candidateContract = null;
     conflict = false;
-      baseSnapshot = structuredClone(treeState.snapshot);
+      baseSnapshot = $state.snapshot(treeState.snapshot);
       baseRevision = treeState.snapshot.revision;
       baseDigest = treeState.snapshot.digest;
-      await toolchain?.setSnapshot(treeState.snapshot);
+      await toolchain?.setSnapshot(treeState.snapshot, treeState.contract.schema_bundle);
       source = treeState.snapshot.entries[selectedPath]?.content ?? "";
       diagnostics = [];
       status = `Committed revision ${treeState.snapshot.revision}.`;
@@ -210,7 +210,7 @@
     baseSnapshot = structuredClone(remote.snapshot);
     baseRevision = remote.snapshot.revision;
     baseDigest = remote.snapshot.digest;
-    await toolchain.setSnapshot(remote.snapshot);
+    await toolchain.setSnapshot(remote.snapshot, remote.contract.schema_bundle);
     try {
       const candidate = await toolchain.applyChanges(localChanges);
       draftChanges = localChanges;
diff --git a/web/workspace/src/lib/workspace/config-source/completion.ts b/web/workspace/src/lib/workspace/config-source/completion.ts
new file mode 100644
index 00000000..8467bdb2
--- /dev/null
+++ b/web/workspace/src/lib/workspace/config-source/completion.ts
@@ -0,0 +1,57 @@
+import type { CompletionResult } from "@codemirror/autocomplete";
+
+export type ConfigSourceCompletionResult = {
+  from: number;
+  items: ConfigSourceCompletionItem[];
+};
+
+type ConfigSourceCompletionItem = {
+  label: string;
+  kind: string;
+  detail: string | null;
+  priority: number;
+};
+
+export function toCodeMirrorCompletion(
+  source: string,
+  result: ConfigSourceCompletionResult | null,
+): CompletionResult | null {
+  if (!result) return null;
+  return {
+    from: utf8ByteOffsetToUtf16(source, result.from),
+    options: result.items.map((item) => ({
+      label: item.label,
+      type: item.kind,
+      detail: item.detail ?? undefined,
+      boost: item.priority,
+    })),
+  };
+}
+
+function utf8ByteOffsetToUtf16(source: string, byteOffset: number): number {
+  if (!Number.isSafeInteger(byteOffset) || byteOffset < 0) {
+    throw new RangeError(
+      "completion byte offset must be a non-negative integer",
+    );
+  }
+
+  let bytes = 0;
+  let utf16 = 0;
+  for (const character of source) {
+    if (bytes === byteOffset) return utf16;
+    const codePoint = character.codePointAt(0)!;
+    bytes += codePoint <= 0x7f
+      ? 1
+      : codePoint <= 0x7ff
+      ? 2
+      : codePoint <= 0xffff
+      ? 3
+      : 4;
+    utf16 += character.length;
+    if (bytes > byteOffset) {
+      throw new RangeError("completion byte offset splits a UTF-8 code point");
+    }
+  }
+  if (bytes === byteOffset) return utf16;
+  throw new RangeError("completion byte offset is outside the source");
+}
diff --git a/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm.d.ts b/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm.d.ts
index af61ca25..3868c368 100644
--- a/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm.d.ts
+++ b/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm.d.ts
@@ -19,6 +19,8 @@ export function formatSource(source: string): string;
 
 export function format_source(source: string): string;
 
+export function set_schema_bundle(schema_bundle: any): void;
+
 export function set_snapshot(snapshot: any): void;
 
 export type InitInput = RequestInfo | URL | Response | BufferSource | WebAssembly.Module;
@@ -33,6 +35,7 @@ export interface InitOutput {
     readonly evaluate_current: (a: any) => [number, number, number];
     readonly evaluate_snapshot: (a: any, b: any) => [number, number, number];
     readonly format_source: (a: number, b: number) => [number, number, number, number];
+    readonly set_schema_bundle: (a: any) => [number, number];
     readonly set_snapshot: (a: any) => [number, number];
     readonly formatSource: (a: number, b: number) => [number, number];
     readonly __wbindgen_malloc: (a: number, b: number) => number;
diff --git a/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm.js b/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm.js
index 9fc330c8..96db090e 100644
--- a/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm.js
+++ b/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm.js
@@ -143,6 +143,16 @@ export function format_source(source) {
     }
 }
 
+/**
+ * @param {any} schema_bundle
+ */
+export function set_schema_bundle(schema_bundle) {
+    const ret = wasm.set_schema_bundle(schema_bundle);
+    if (ret[1]) {
+        throw takeFromExternrefTable0(ret[0]);
+    }
+}
+
 /**
  * @param {any} snapshot
  */
diff --git a/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm_bg.wasm b/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm_bg.wasm
index 5f621ea3..e4e3e6f6 100644
Binary files a/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm_bg.wasm and b/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm_bg.wasm differ
diff --git a/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm_bg.wasm.d.ts b/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm_bg.wasm.d.ts
index 361b58be..cf8f17e8 100644
--- a/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm_bg.wasm.d.ts
+++ b/web/workspace/src/lib/workspace/config-source/generated/config_source_wasm_bg.wasm.d.ts
@@ -9,6 +9,7 @@ export const compose_schema_bundle: (a: any) => [number, number, number];
 export const evaluate_current: (a: any) => [number, number, number];
 export const evaluate_snapshot: (a: any, b: any) => [number, number, number];
 export const format_source: (a: number, b: number) => [number, number, number, number];
+export const set_schema_bundle: (a: any) => [number, number];
 export const set_snapshot: (a: any) => [number, number];
 export const formatSource: (a: number, b: number) => [number, number];
 export const __wbindgen_malloc: (a: number, b: number) => number;
diff --git a/web/workspace/src/lib/workspace/config-source/toolchain-message.ts b/web/workspace/src/lib/workspace/config-source/toolchain-message.ts
new file mode 100644
index 00000000..d9d376b9
--- /dev/null
+++ b/web/workspace/src/lib/workspace/config-source/toolchain-message.ts
@@ -0,0 +1,3 @@
+export function jsonWorkerMessage<T>(request: T): T {
+  return JSON.parse(JSON.stringify(request)) as T;
+}
diff --git a/web/workspace/src/lib/workspace/config-source/toolchain.ts b/web/workspace/src/lib/workspace/config-source/toolchain.ts
index cf27ed0f..311e99c8 100644
--- a/web/workspace/src/lib/workspace/config-source/toolchain.ts
+++ b/web/workspace/src/lib/workspace/config-source/toolchain.ts
@@ -1,5 +1,19 @@
-import type { ConfigDiagnostic, ConfigTreeChange, ConfigTreeSnapshot, ToolchainContract } from "./types.ts";
-import type { ConfigSourceWorkerRequest, ConfigSourceWorkerResponse } from "./toolchain.worker.ts";
+import type {
+  ConfigDiagnostic,
+  ConfigTreeChange,
+  ConfigTreeSnapshot,
+  ToolchainContract,
+  WorkspaceConfigSchemaBundle,
+} from "./types.ts";
+import { jsonWorkerMessage } from "./toolchain-message.ts";
+import {
+  type ConfigSourceCompletionResult,
+  toCodeMirrorCompletion,
+} from "./completion.ts";
+import type {
+  ConfigSourceWorkerRequest,
+  ConfigSourceWorkerResponse,
+} from "./toolchain.worker.ts";
 
 type Command =
   | Omit<Extract<ConfigSourceWorkerRequest, { kind: "set_snapshot" }>, "id">
@@ -13,26 +27,42 @@ type Command =
 export class ConfigSourceToolchain {
   #worker: Worker;
   #nextId = 1;
-  #pending = new Map<number, { resolve: (value: unknown) => void; reject: (reason: unknown) => void }>();
+  #pending = new Map<
+    number,
+    { resolve: (value: unknown) => void; reject: (reason: unknown) => void }
+  >();
 
-  constructor(worker = new Worker(new URL("./toolchain.worker.ts", import.meta.url), { type: "module" })) {
+  constructor(
+    worker = new Worker(new URL("./toolchain.worker.ts", import.meta.url), {
+      type: "module",
+    }),
+  ) {
     this.#worker = worker;
-    worker.addEventListener("message", (event: MessageEvent<ConfigSourceWorkerResponse>) => {
-      const pending = this.#pending.get(event.data.id);
-      if (!pending) return;
-      this.#pending.delete(event.data.id);
-      if (event.data.ok) pending.resolve(event.data.result);
-      else pending.reject(event.data.error);
-    });
+    worker.addEventListener(
+      "message",
+      (event: MessageEvent<ConfigSourceWorkerResponse>) => {
+        const pending = this.#pending.get(event.data.id);
+        if (!pending) return;
+        this.#pending.delete(event.data.id);
+        if (event.data.ok) pending.resolve(event.data.result);
+        else pending.reject(event.data.error);
+      },
+    );
   }
 
-  setSnapshot(snapshot: ConfigTreeSnapshot): Promise<void> {
-    return this.#request({ kind: "set_snapshot", snapshot });
+  setSnapshot(
+    snapshot: ConfigTreeSnapshot,
+    schemaBundle: WorkspaceConfigSchemaBundle,
+  ): Promise<void> {
+    return this.#request({ kind: "set_snapshot", snapshot, schemaBundle });
   }
   applyChanges(changes: ConfigTreeChange[]): Promise<ConfigTreeSnapshot> {
     return this.#request({ kind: "apply_changes", changes });
   }
-  changesBetween(base: ConfigTreeSnapshot, candidate: ConfigTreeSnapshot): Promise<ConfigTreeChange[]> {
+  changesBetween(
+    base: ConfigTreeSnapshot,
+    candidate: ConfigTreeSnapshot,
+  ): Promise<ConfigTreeChange[]> {
     return this.#request({ kind: "changes_between", base, candidate });
   }
   analyze(path: string, source?: string): Promise<ConfigDiagnostic[]> {
@@ -41,22 +71,40 @@ export class ConfigSourceToolchain {
   evaluate(contract: ToolchainContract) {
     return this.#request({ kind: "evaluate", contract });
   }
-  complete(path: string, source: string, utf16Offset: number, explicit = false): Promise<import("@codemirror/autocomplete").CompletionResult | null> {
-    return this.#request({ kind: "complete", path, source, utf16Offset, explicit });
+  async complete(
+    path: string,
+    source: string,
+    utf16Offset: number,
+    explicit = false,
+  ): Promise<import("@codemirror/autocomplete").CompletionResult | null> {
+    const result = await this.#request<ConfigSourceCompletionResult | null>({
+      kind: "complete",
+      path,
+      source,
+      utf16Offset,
+      explicit,
+    });
+    return toCodeMirrorCompletion(source, result);
   }
   format(source: string): Promise<string> {
     return this.#request({ kind: "format", source });
   }
   close(): void {
     this.#worker.terminate();
-    for (const pending of this.#pending.values()) pending.reject(new Error("config source toolchain was closed"));
+    for (const pending of this.#pending.values()) {
+      pending.reject(new Error("config source toolchain was closed"));
+    }
     this.#pending.clear();
   }
   #request<T>(request: Command): Promise<T> {
     const id = this.#nextId++;
+    const message = jsonWorkerMessage({ ...request, id });
     return new Promise<T>((resolve, reject) => {
-      this.#pending.set(id, { resolve: (value) => resolve(value as T), reject });
-      this.#worker.postMessage({ ...request, id });
+      this.#pending.set(id, {
+        resolve: (value) => resolve(value as T),
+        reject,
+      });
+      this.#worker.postMessage(message);
     });
   }
 }
diff --git a/web/workspace/src/lib/workspace/config-source/toolchain.worker.ts b/web/workspace/src/lib/workspace/config-source/toolchain.worker.ts
index 32885cb7..9095114e 100644
--- a/web/workspace/src/lib/workspace/config-source/toolchain.worker.ts
+++ b/web/workspace/src/lib/workspace/config-source/toolchain.worker.ts
@@ -5,17 +5,30 @@ import init, {
   complete_current,
   evaluate_current,
   format_source,
+  set_schema_bundle,
   set_snapshot,
 } from "./generated/config_source_wasm.js";
 import type { ConfigTreeChange } from "./types.ts";
 
 export type ConfigSourceWorkerRequest =
-  | { id: number; kind: "set_snapshot"; snapshot: unknown }
+  | {
+    id: number;
+    kind: "set_snapshot";
+    snapshot: unknown;
+    schemaBundle: unknown;
+  }
   | { id: number; kind: "apply_changes"; changes: ConfigTreeChange[] }
   | { id: number; kind: "changes_between"; base: unknown; candidate: unknown }
   | { id: number; kind: "analyze"; path: string; source?: string }
   | { id: number; kind: "evaluate"; contract: unknown }
-  | { id: number; kind: "complete"; path: string; source: string; utf16Offset: number; explicit: boolean }
+  | {
+    id: number;
+    kind: "complete";
+    path: string;
+    source: string;
+    utf16Offset: number;
+    explicit: boolean;
+  }
   | { id: number; kind: "format"; source: string };
 
 export type ConfigSourceWorkerResponse =
@@ -25,7 +38,9 @@ export type ConfigSourceWorkerResponse =
 const ready = init();
 let snapshot: unknown = null;
 
-self.onmessage = async (event: MessageEvent<ConfigSourceWorkerRequest>): Promise<void> => {
+self.onmessage = async (
+  event: MessageEvent<ConfigSourceWorkerRequest>,
+): Promise<void> => {
   const request = event.data;
   try {
     await ready;
@@ -34,6 +49,7 @@ self.onmessage = async (event: MessageEvent<ConfigSourceWorkerRequest>): Promise
       case "set_snapshot":
         snapshot = request.snapshot;
         set_snapshot(request.snapshot);
+        set_schema_bundle(request.schemaBundle);
         result = null;
         break;
       case "apply_changes":
@@ -44,14 +60,21 @@ self.onmessage = async (event: MessageEvent<ConfigSourceWorkerRequest>): Promise
         result = changes_between(request.base, request.candidate);
         break;
       case "analyze":
-        if (!snapshot) throw new Error("config source snapshot is not initialized");
+        if (!snapshot) {
+          throw new Error("config source snapshot is not initialized");
+        }
         result = analyze_snapshot(snapshot, request.path, request.source);
         break;
       case "evaluate":
         result = evaluate_current(request.contract);
         break;
       case "complete":
-        result = complete_current(request.path, request.source, request.utf16Offset, request.explicit);
+        result = complete_current(
+          request.path,
+          request.source,
+          request.utf16Offset,
+          request.explicit,
+        );
         break;
       case "format":
         result = format_source(request.source);
@@ -59,6 +82,10 @@ self.onmessage = async (event: MessageEvent<ConfigSourceWorkerRequest>): Promise
     }
     self.postMessage({ id: request.id, ok: true, result });
   } catch (error) {
-    self.postMessage({ id: request.id, ok: false, error: error instanceof Error ? error.message : error });
+    self.postMessage({
+      id: request.id,
+      ok: false,
+      error: error instanceof Error ? error.message : error,
+    });
   }
 };
diff --git a/web/workspace/src/lib/workspace/console/worker-console.ui.test.ts b/web/workspace/src/lib/workspace/console/worker-console.ui.test.ts
index 7199b611..0e7c53da 100644
--- a/web/workspace/src/lib/workspace/console/worker-console.ui.test.ts
+++ b/web/workspace/src/lib/workspace/console/worker-console.ui.test.ts
@@ -459,11 +459,11 @@ Deno.test("Decodal source editor keeps imperative EditorView out of reactive sta
   );
 
   assert(
-    editor.includes("let view: EditorView | null = null") &&
-      !editor.includes("$state<EditorView") &&
+    editor.includes("let view = $state.raw<EditorView | null>(null)") &&
+      editor.includes("untrack(() => view)") &&
       editor.includes("untrack(() => value)") &&
       editor.includes("untrack(() => onChange)"),
-    "CodeMirror EditorView must not be reactive state; otherwise mount cleanup can loop forever",
+    "CodeMirror EditorView must not be deep reactive or tracked by the mount effect; otherwise cleanup can loop forever",
   );
 });
 
diff --git a/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte b/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
index 20e58e61..4f4b5667 100644
--- a/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
+++ b/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
@@ -1,8 +1,10 @@
 <script lang="ts">
   import { untrack } from 'svelte';
   import { autocompletion, type CompletionContext, type CompletionResult } from '@codemirror/autocomplete';
-  import { EditorState } from '@codemirror/state';
+  import { HighlightStyle, syntaxHighlighting } from '@codemirror/language';
+  import { Compartment, EditorState } from '@codemirror/state';
   import { EditorView, keymap, lineNumbers, highlightActiveLine, drawSelection } from '@codemirror/view';
+  import { tags } from '@lezer/highlight';
   import { decodal } from 'decodal-codemirror';
 
   let {
@@ -20,25 +22,43 @@
   } = $props();
 
   let host = $state<HTMLDivElement | null>(null);
-  let view: EditorView | null = null;
+  let view = $state.raw<EditorView | null>(null);
+  const readonlyCompartment = new Compartment();
+
+  const syntaxTheme = HighlightStyle.define([
+    { tag: tags.keyword, color: 'var(--accent)', fontWeight: '700' },
+    { tag: tags.variableName, color: 'var(--code)' },
+    { tag: [tags.bool, tags.number], color: 'var(--warning)' },
+    { tag: [tags.string, tags.regexp], color: 'var(--success)' },
+    { tag: tags.lineComment, color: 'var(--text-muted)', fontStyle: 'italic' },
+    { tag: tags.operator, color: 'var(--danger)' },
+    { tag: [tags.brace, tags.squareBracket, tags.paren, tags.punctuation], color: 'var(--accent-muted)' },
+  ]);
 
   const theme = EditorView.theme({
     '&': {
-      border: '1px solid var(--border-subtle)',
+      border: '1px solid var(--line)',
       borderRadius: '0.75rem',
       minHeight: '24rem',
-      background: 'var(--surface-2)',
-      color: 'var(--text-primary)',
+      background: 'var(--bg-raised)',
+      color: 'var(--text)',
       fontSize: '0.9rem',
     },
+    '&.cm-focused': { outline: '1px solid var(--accent-muted)', outlineOffset: '-1px' },
     '.cm-scroller': { fontFamily: 'var(--font-mono)', minHeight: '24rem' },
-    '.cm-content': { padding: '0.75rem 0' },
-    '.cm-gutters': { background: 'var(--surface-2)', color: 'var(--text-muted)' },
-    '.cm-activeLine': { backgroundColor: 'rgba(125, 211, 252, 0.08)' },
+    '.cm-content': { padding: '0.75rem 0', caretColor: 'var(--text-strong)' },
+    '.cm-cursor, .cm-dropCursor': { borderLeftColor: 'var(--text-strong)', borderLeftWidth: '2px' },
+    '&.cm-focused > .cm-scroller > .cm-selectionLayer .cm-selectionBackground, .cm-selectionBackground, .cm-content ::selection': {
+      backgroundColor: 'var(--interactive-selected)',
+    },
+    '.cm-gutters': { background: 'var(--bg-raised)', color: 'var(--text-muted)', borderColor: 'var(--line)' },
+    '.cm-activeLine, .cm-activeLineGutter': { backgroundColor: 'var(--interactive-hover)' },
+    '.cm-tooltip': { background: 'var(--bg-raised)', color: 'var(--text)', borderColor: 'var(--line-strong)' },
+    '.cm-tooltip-autocomplete > ul > li[aria-selected]': { background: 'var(--interactive-selected)', color: 'var(--text-strong)' },
   });
 
   $effect(() => {
-    if (!host || view) return;
+    if (!host || untrack(() => view)) return;
     const initialValue = untrack(() => value);
     const initialReadonly = untrack(() => readonly);
     const handleChange = untrack(() => onChange);
@@ -51,14 +71,17 @@
           lineNumbers(),
           drawSelection(),
           highlightActiveLine(),
-          decodal(),
+          decodal({ highlight: false }),
+          syntaxHighlighting(syntaxTheme),
           ...(handleComplete ? [autocompletion({ override: [async (context: CompletionContext) => {
             const doc = context.state.doc.toString();
             return await handleComplete(doc, context.pos, context.explicit);
           }] })] : []),
           keymap.of([]),
-          EditorState.readOnly.of(initialReadonly),
-          EditorView.editable.of(!initialReadonly),
+          readonlyCompartment.of([
+            EditorState.readOnly.of(initialReadonly),
+            EditorView.editable.of(!initialReadonly),
+          ]),
           EditorView.updateListener.of((update) => {
             if (update.docChanged) handleChange(update.state.doc.toString());
           }),
@@ -73,6 +96,18 @@
     };
   });
 
+  $effect(() => {
+    const editor = view;
+    const nextReadonly = readonly;
+    if (!editor) return;
+    editor.dispatch({
+      effects: readonlyCompartment.reconfigure([
+        EditorState.readOnly.of(nextReadonly),
+        EditorView.editable.of(!nextReadonly),
+      ]),
+    });
+  });
+
   $effect(() => {
     if (!view) return;
     const current = view.state.doc.toString();
diff --git a/web/workspace/test/config-source/editor-state.test.ts b/web/workspace/test/config-source/editor-state.test.ts
new file mode 100644
index 00000000..12f16926
--- /dev/null
+++ b/web/workspace/test/config-source/editor-state.test.ts
@@ -0,0 +1,75 @@
+declare const Deno: {
+  test(name: string, fn: () => Promise<void> | void): void;
+  readTextFile(path: URL): Promise<string>;
+};
+
+function assert(condition: unknown, message: string): asserts condition {
+  if (!condition) throw new Error(message);
+}
+
+Deno.test("config editor snapshots Svelte proxies before cloning baselines", async () => {
+  const source = await Deno.readTextFile(
+    new URL(
+      "../../src/lib/workspace/config-source/ConfigSourceEditor.svelte",
+      import.meta.url,
+    ),
+  );
+
+  assert(
+    source.includes("$state.raw<WorkspaceConfigTreeResponse"),
+    "the immutable config baseline should not be wrapped in another deep proxy",
+  );
+  assert(
+    source.includes("$state.snapshot(treeState.snapshot)"),
+    "reactive tree snapshots should be converted to plain values before reuse",
+  );
+  assert(
+    !source.includes("structuredClone(treeState.snapshot)"),
+    "structuredClone must never receive a Svelte state proxy",
+  );
+  assert(
+    source.includes("toolchain?.setSnapshot(") &&
+      source.includes("treeState.contract.schema_bundle") &&
+      source.includes("remote.contract.schema_bundle"),
+    "the authoritative schema bundle should be installed with every snapshot",
+  );
+});
+
+Deno.test("Decodal editor follows readonly prop changes after mount", async () => {
+  const source = await Deno.readTextFile(
+    new URL(
+      "../../src/lib/workspace/settings/DecodalSourceEditor.svelte",
+      import.meta.url,
+    ),
+  );
+
+  assert(
+    source.includes("let view = $state.raw<EditorView | null>(null)") &&
+      source.includes("if (!host || untrack(() => view)) return"),
+    "imperative EditorView should avoid deep proxying and remain outside the mount effect dependency graph",
+  );
+  assert(
+    source.includes("new Compartment()") &&
+      source.includes("readonlyCompartment.reconfigure") &&
+      source.includes("EditorView.editable.of(!nextReadonly)"),
+    "readonly and editable facets should be reconfigured when the prop changes",
+  );
+  assert(
+    source.includes("syntaxHighlighting(syntaxTheme)") &&
+      source.includes("tags.keyword") &&
+      source.includes("tags.string"),
+    "Decodal tokens should use an explicit syntax theme",
+  );
+  assert(
+    source.includes(".cm-cursor, .cm-dropCursor") &&
+      source.includes(".cm-selectionBackground") &&
+      source.includes("var(--interactive-selected)"),
+    "cursor and selection should be visible against the workspace theme",
+  );
+  assert(
+    !source.includes("--surface-2") &&
+      !source.includes("--text-primary") &&
+      !source.includes("--border-subtle"),
+    "CodeMirror theme must use workspace tokens that actually exist",
+  );
+});
diff --git a/web/workspace/test/config-source/toolchain.test.ts b/web/workspace/test/config-source/toolchain.test.ts
new file mode 100644
index 00000000..2140fb02
--- /dev/null
+++ b/web/workspace/test/config-source/toolchain.test.ts
@@ -0,0 +1,109 @@
+declare const Deno: {
+  test(name: string, fn: () => Promise<void> | void): void;
+  readTextFile(path: URL): Promise<string>;
+};
+
+import { toCodeMirrorCompletion } from "../../src/lib/workspace/config-source/completion.ts";
+import { jsonWorkerMessage } from "../../src/lib/workspace/config-source/toolchain-message.ts";
+
+function assert(condition: unknown, message: string): asserts condition {
+  if (!condition) throw new Error(message);
+}
+
+Deno.test("toolchain converts reactive-like proxies to plain Worker messages", async () => {
+  const snapshot = new Proxy(
+    {
+      revision: 1,
+      digest: "sha256:test",
+      entries: {},
+    },
+    {},
+  );
+  const request = {
+    id: 1,
+    kind: "set_snapshot" as const,
+    snapshot,
+  };
+
+  let cloneRejected = false;
+  try {
+    structuredClone(request);
+  } catch (error) {
+    cloneRejected = error instanceof DOMException &&
+      error.name === "DataCloneError";
+  }
+  assert(
+    cloneRejected,
+    "fixture should reproduce the Worker postMessage clone failure",
+  );
+
+  const message = jsonWorkerMessage(request);
+  assert(
+    message.snapshot !== snapshot,
+    "snapshot should be detached from the Proxy",
+  );
+  structuredClone(message);
+
+  const source = await Deno.readTextFile(
+    new URL(
+      "../../src/lib/workspace/config-source/toolchain.ts",
+      import.meta.url,
+    ),
+  );
+  assert(
+    source.includes("const message = jsonWorkerMessage({ ...request, id })") &&
+      source.includes("this.#worker.postMessage(message)"),
+    "ConfigSourceToolchain should normalize every command at the Worker boundary",
+  );
+  const workerSource = await Deno.readTextFile(
+    new URL(
+      "../../src/lib/workspace/config-source/toolchain.worker.ts",
+      import.meta.url,
+    ),
+  );
+  assert(
+    workerSource.includes("set_schema_bundle(request.schemaBundle)"),
+    "Config Source worker should install the WorkspaceConfigSchema global contract",
+  );
+});
+
+Deno.test("toolchain adapts WASM completion items and byte offsets for CodeMirror", () => {
+  const source = "let 名 = tru";
+  const result = toCodeMirrorCompletion(source, {
+    from: new TextEncoder().encode("let 名 = ").length,
+    items: [
+      {
+        label: "true",
+        kind: "constant",
+        detail: "Bool",
+        priority: 20,
+      },
+    ],
+  });
+
+  assert(result !== null, "WASM completion should produce a CodeMirror result");
+  assert(
+    result.from === "let 名 = ".length,
+    "byte offsets should become UTF-16 offsets",
+  );
+  assert(
+    result.options.length === 1,
+    "WASM items should become CodeMirror options",
+  );
+  assert(
+    result.options[0].label === "true",
+    "completion label should be preserved",
+  );
+  assert(
+    result.options[0].type === "constant",
+    "completion kind should become the icon type",
+  );
+  assert(
+    result.options[0].detail === "Bool",
+    "completion detail should be preserved",
+  );
+  assert(
+    result.options[0].boost === 20,
+    "completion priority should become its boost",
+  );
+});
diff --git a/web/workspace/test/config-source/wasm-parity.test.ts b/web/workspace/test/config-source/wasm-parity.test.ts
index 41df078b..47828453 100644
--- a/web/workspace/test/config-source/wasm-parity.test.ts
+++ b/web/workspace/test/config-source/wasm-parity.test.ts
@@ -3,8 +3,11 @@
 import { assertEquals } from "jsr:@std/assert";
 import init, {
   analyze_snapshot,
+  complete_current,
   compose_schema_bundle,
   evaluate_snapshot,
+  set_schema_bundle,
+  set_snapshot,
 } from "../../src/lib/workspace/config-source/generated/config_source_wasm.js";
 import type {
   ConfigTreeSnapshot,
@@ -241,3 +244,74 @@ Deno.test("generated WASM preserves native Decodal 0.4 diagnostic semantics", ()
     assertEquals(diagnostic.span.end_byte > diagnostic.span.start_byte, true);
   }
 });
+
+Deno.test("generated WASM returns completion items for the editor adapter", () => {
+  const source = 'import "./"';
+  set_snapshot({
+    ...snapshot,
+    entries: {
+      ...snapshot.entries,
+      "workspace.dcdl": {
+        ...snapshot.entries["workspace.dcdl"],
+        content: source,
+      },
+    },
+  });
+  const result = complete_current(
+    "workspace.dcdl",
+    source,
+    source.length - 1,
+    true,
+  ) as {
+    from: number;
+    items: Array<{ label: string; kind: string }>;
+  };
+
+  assertEquals(result.from, 8);
+  assertEquals(result.items[0].label, "./lib/value.dcdl");
+  assertEquals(result.items[0].kind, "file");
+});
+
+Deno.test("generated WASM completes asserted WorkspaceConfigSchema keys", () => {
+  const bareSource = "{ pro }";
+  const source = "{ pro } as WorkspaceConfigSchema";
+  const cursor = source.indexOf("pro") + 3;
+  set_snapshot({
+    ...snapshot,
+    entries: {
+      ...snapshot.entries,
+      "workspace.dcdl": {
+        ...snapshot.entries["workspace.dcdl"],
+        content: source,
+      },
+    },
+  });
+  set_schema_bundle({
+    contributions: [],
+    source: "{ profile = { default_profile = String; }; prompts = {}; }",
+    fingerprint: "sha256:test-schema",
+  });
+  const bare = complete_current(
+    "workspace.dcdl",
+    bareSource,
+    bareSource.indexOf("pro") + 3,
+    true,
+  ) as { items: Array<{ label: string }> } | null;
+  assertEquals(
+    bare?.items.some((item) => item.label === "profile") ?? false,
+    false,
+  );
+
+  const result = complete_current(
+    "workspace.dcdl",
+    source,
+    cursor,
+    true,
+  ) as {
+    from: number;
+    items: Array<{ label: string; kind: string }>;
+  };
+
+  assertEquals(result.from, 2);
+  assertEquals(result.items.some((item) => item.label === "profile"), true);
+});