feat(workspace): multi-scope workspace reads (#1117)

* feat(workspace): multi-scope workspace reads

Adds the ability for a workspace to read from multiple user scopes
while keeping writes isolated to the primary scope. Configuration
via WORKSPACE_READ_SCOPES env var (comma-separated user IDs).

Includes identity file isolation (read_primary), multi-scope search,
list, and read operations, WorkspaceConfig refactor, and comprehensive
integration tests.

* fix: address review feedback for multi-scope workspace reads

- fix(memory): deduplicate timezone parsing for daily_log target
  parse_timezone was called twice when target was "daily_log" without a
  layer — once in path resolution, again in the fallback. Now computed
  once and reused.

- fix(config): add character validation for WORKSPACE_READ_SCOPES and
  layer scopes — both enforce [a-zA-Z0-9_-] to prevent path traversal
  or injection via scope strings used as user_id in SQL queries.

- fix(config): use chars().take(32) instead of byte-index slicing for
  scope length error messages (UTF-8 safety).

- fix(error): remove unused WorkspaceError::NotFound variant

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

* style: downgrade search log to debug, add comments on list iteration

- Downgrade hybrid_search_multi tracing::info! to debug! — fires on
  every multi-scope search with the default backend, too noisy for info
- Add comments explaining why list/list_all iterate per-scope instead
  of using _multi trait methods (identity path filtering needs scope
  attribution that merged results lose)

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

---------

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

src/config/mod.rs

@@ -24,7 +24,7 @@ mod skills;
 mod transcription;
 mod tunnel;
 mod wasm;
-mod workspace;
+pub(crate) mod workspace;
 
 use std::collections::HashMap;
 use std::sync::{LazyLock, Mutex, Once};
@@ -178,9 +178,7 @@ impl Config {
             },
             transcription: TranscriptionConfig::default(),
             search: WorkspaceSearchConfig::default(),
-            workspace: WorkspaceConfig {
-                memory_layers: vec![],
-            },
+            workspace: WorkspaceConfig::default(),
             observability: crate::observability::ObservabilityConfig::default(),
             relay: None,
         }
@@ -313,11 +311,14 @@ impl Config {
 
         let tunnel = TunnelConfig::resolve(settings)?;
         let channels = ChannelsConfig::resolve(settings, &owner_id)?;
+
+        // Resolve workspace config using the gateway user_id for default layers.
         let workspace_user_id = channels
             .gateway
             .as_ref()
-            .map(|gw| gw.user_id.clone())
-            .unwrap_or_else(|| "default".to_string());
+            .map(|gw| gw.user_id.as_str())
+            .unwrap_or("default");
+        let workspace = WorkspaceConfig::resolve(workspace_user_id)?;
 
         Ok(Self {
             owner_id: owner_id.clone(),
@@ -339,7 +340,7 @@ impl Config {
             skills: SkillsConfig::resolve()?,
             transcription: TranscriptionConfig::resolve(settings)?,
             search: WorkspaceSearchConfig::resolve()?,
-            workspace: WorkspaceConfig::resolve(&workspace_user_id)?,
+            workspace,
             observability: crate::observability::ObservabilityConfig {
                 backend: std::env::var("OBSERVABILITY_BACKEND").unwrap_or_else(|_| "none".into()),
             },

src/config/workspace.rs

@@ -2,18 +2,29 @@ use crate::config::helpers::optional_env;
 use crate::error::ConfigError;
 use crate::workspace::layer::MemoryLayer;
 
-/// Workspace memory configuration.
+/// Workspace-level configuration (memory layers, read scopes).
 ///
-/// Controls memory layer definitions for privacy-aware writes.
-/// Layers are parsed from the `MEMORY_LAYERS` env var (JSON array)
-/// or default to a single private layer scoped to the gateway user.
-#[derive(Debug, Clone)]
+/// Parsed from environment variables. Lives outside of `GatewayConfig`
+/// so that non-gateway channels can eventually use the same settings.
+#[derive(Debug, Clone, Default)]
 pub struct WorkspaceConfig {
+    /// Memory layer definitions (JSON in `MEMORY_LAYERS` env var, or defaults).
     pub memory_layers: Vec<MemoryLayer>,
+    /// Additional user scopes for workspace reads.
+    ///
+    /// When set, the workspace can read (search, read, list) from these
+    /// additional user scopes while writes remain isolated to the primary
+    /// `user_id`. Parsed from `WORKSPACE_READ_SCOPES` (comma-separated).
+    pub read_scopes: Vec<String>,
 }
 
 impl WorkspaceConfig {
-    pub(crate) fn resolve(user_id: &str) -> Result<Self, ConfigError> {
+    /// Resolve workspace config from environment variables.
+    ///
+    /// `user_id` is used to derive default memory layers when `MEMORY_LAYERS`
+    /// is not set.
+    pub fn resolve(user_id: &str) -> Result<Self, ConfigError> {
+        // --- Memory layers ---
         let memory_layers: Vec<MemoryLayer> = match optional_env("MEMORY_LAYERS")? {
             Some(json_str) => {
                 serde_json::from_str(&json_str).map_err(|e| ConfigError::InvalidValue {
@@ -57,6 +68,20 @@ impl WorkspaceConfig {
                     message: format!("layer '{}' has an empty scope", layer.name),
                 });
             }
+            if !layer
+                .scope
+                .chars()
+                .all(|c| c.is_ascii_alphanumeric() || c == '_' || c == '-')
+            {
+                return Err(ConfigError::InvalidValue {
+                    key: "MEMORY_LAYERS".to_string(),
+                    message: format!(
+                        "layer '{}' scope '{}' contains invalid characters \
+                         (allowed: a-z, A-Z, 0-9, _, -)",
+                        layer.name, layer.scope
+                    ),
+                });
+            }
         }
 
         // Check for duplicate layer names
@@ -72,7 +97,43 @@ impl WorkspaceConfig {
             }
         }
 
-        Ok(Self { memory_layers })
+        // --- Read scopes ---
+        let read_scopes: Vec<String> = optional_env("WORKSPACE_READ_SCOPES")?
+            .map(|s| {
+                s.split(',')
+                    .map(|s| s.trim().to_string())
+                    .filter(|s| !s.is_empty())
+                    .collect()
+            })
+            .unwrap_or_default();
+
+        for scope in &read_scopes {
+            if scope.len() > 128 {
+                let prefix: String = scope.chars().take(32).collect();
+                return Err(ConfigError::InvalidValue {
+                    key: "WORKSPACE_READ_SCOPES".to_string(),
+                    message: format!("scope '{prefix}...' exceeds 128 characters"),
+                });
+            }
+            if !scope
+                .chars()
+                .all(|c| c.is_ascii_alphanumeric() || c == '_' || c == '-')
+            {
+                return Err(ConfigError::InvalidValue {
+                    key: "WORKSPACE_READ_SCOPES".to_string(),
+                    message: format!(
+                        "scope '{}' contains invalid characters \
+                         (allowed: a-z, A-Z, 0-9, _, -)",
+                        scope
+                    ),
+                });
+            }
+        }
+
+        Ok(Self {
+            memory_layers,
+            read_scopes,
+        })
     }
 }