fix(security): address review feedback on cross-channel approval checks

1. thread_ops.rs: Remove .or(Some(&*message.channel)) fallback in
   maybe_hydrate_thread() so that when source_channel is NULL in the DB,
   it stays None rather than being stamped with the requesting channel.
   This preserves the fail-closed behavior of is_approval_authorized().

2. libsql_migrations.rs: Remove source_channel from base SCHEMA to
   eliminate duplicate column definition. The column is now added solely
   by V14 migration, preventing fresh databases from failing on startup.

3. wasm/setup.rs: Expand RESERVED_CHANNEL_NAMES to cover all built-in
   channels (http, signal, slack-relay, secret_save) and add a dynamic
   collision check against already-registered channel names passed from
   the startup sequence.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

src/agent/thread_ops.rs

@@ -146,7 +146,7 @@ impl Agent {
         } else {
             None
         };
-        let effective_source_channel = db_source_channel.as_deref().or(Some(&*message.channel));
+        let effective_source_channel = db_source_channel.as_deref();
 
         let session_id = {
             let sess = session.lock().await;

src/channels/wasm/setup.rs

@@ -34,6 +34,7 @@ pub async fn setup_wasm_channels(
     secrets_store: &Option<Arc<dyn SecretsStore + Send + Sync>>,
     extension_manager: Option<&Arc<ExtensionManager>>,
     database: Option<&Arc<dyn Database>>,
+    registered_channel_names: &[String],
 ) -> Option<WasmChannelSetup> {
     let runtime = match WasmChannelRuntime::new(WasmChannelRuntimeConfig::default()) {
         Ok(r) => Arc::new(r),
@@ -74,7 +75,19 @@ pub async fn setup_wasm_channels(
     // Reserved channel names that WASM modules must not claim.
     // A malicious module could otherwise register as a trusted built-in
     // channel and bypass cross-channel authorization checks.
-    const RESERVED_CHANNEL_NAMES: &[&str] = &["web", "gateway", "cli", "repl"];
+    // This list must cover every built-in channel name to prevent a WASM
+    // module from impersonating a built-in and satisfying same-channel
+    // approval checks.
+    const RESERVED_CHANNEL_NAMES: &[&str] = &[
+        "web",
+        "gateway",
+        "cli",
+        "repl",
+        "http",
+        "signal",
+        "slack-relay",
+        "secret_save",
+    ];
 
     for loaded in results.loaded {
         let name_lower = loaded.name().to_ascii_lowercase();
@@ -85,6 +98,19 @@ pub async fn setup_wasm_channels(
             );
             continue;
         }
+        // Also reject any name that collides with an already-registered
+        // channel to prevent a WASM module from shadowing a channel that
+        // was registered earlier in the startup sequence.
+        if registered_channel_names
+            .iter()
+            .any(|n| n.to_ascii_lowercase() == name_lower)
+        {
+            tracing::warn!(
+                channel = %loaded.name(),
+                "Rejected WASM channel that collides with already-registered channel"
+            );
+            continue;
+        }
 
         let (name, channel) = register_channel(
             loaded,

src/db/libsql_migrations.rs

@@ -38,8 +38,7 @@ CREATE TABLE IF NOT EXISTS conversations (
     thread_id TEXT,
     started_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
     last_activity TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
-    metadata TEXT NOT NULL DEFAULT '{}',
-    source_channel TEXT
+    metadata TEXT NOT NULL DEFAULT '{}'
 );
 
 CREATE INDEX IF NOT EXISTS idx_conversations_channel ON conversations(channel);

src/main.rs

@@ -449,6 +449,7 @@ async fn async_main() -> anyhow::Result<()> {
             &components.secrets_store,
             components.extension_manager.as_ref(),
             components.db.as_ref(),
+            &channel_names,
         )
         .await;