feat(workspace): layered memory with sensitivity-based privacy redirect (#1112)

* feat(workspace): layered memory with sensitivity-based privacy redirect

Introduce MemoryLayer type for named memory layers with sensitivity
levels and write permissions. Layers map to synthetic user_id values
in workspace tables, enabling shared/private memory isolation.

- Add MemoryLayer, LayerSensitivity types with default_for_user()
- Add layer-aware write methods (write_to_layer, append_to_layer)
- Add PatternPrivacyClassifier to guard shared layer writes
- Add optional 'layer' parameter to memory_write tool and HTTP API
- Add 'redirected' and 'actual_layer' fields to write response
- Add MEMORY_LAYERS env var (JSON) for layer configuration
- Workspace user_id now derived from GATEWAY_USER_ID (was hardcoded "default")
- 10 integration tests for layered memory operations

Addresses prerequisite for Issue #59 (multi-tenancy).

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: add explicit default to memory_write layer schema

Add "default": "private" to the layer parameter's JSON schema so
LLM tool consumers can see the default without reading code.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* refactor: extract resolve_layer_target to deduplicate layer writes

Consolidate shared layer-lookup, writable check, and privacy
classification logic from write_to_layer and append_to_layer into a
single resolve_layer_target helper.

Flagged on #349 review — the duplication originates in this PR.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: address review feedback on layered memory PR

- Fix email regex pipe bug in TLD character class (privacy.rs)
- Add append support to web memory_write handler via `append` field
- Validate MemoryLayer name/scope: reject empty, check duplicates
- Remove hardcoded 'private' default from tool schema; omit layer
  fields from output when no layer specified
- Document scope isolation risk for multi-tenant (Issue #59)

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: address adversarial review findings

- CRITICAL: fix identity file protection bypass via trailing slash
  (normalize target path before protection checks)
- HIGH: check private layer is writable before privacy redirect
- HIGH: map LayerNotFound/ReadOnly to proper 4xx HTTP status codes
- HIGH: honor `append` field in non-layer HTTP write path
- MEDIUM: remove redundant DB fetch in append_to_layer (narrower
  TOCTOU window)
- MEDIUM: remove dead memory_write_handler from handlers/memory.rs

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* feat: opt-in privacy classifier, force override, confidence scoring

Address review feedback from @zmanian:

- Privacy classifier is now opt-in via with_privacy_classifier() instead
  of always-on. Default hardcoded patterns (doctor, therapy, email, phone)
  had unacceptable false positive rates in household contexts. LLM chooses
  the correct layer via system prompt; regex can't improve on that.
- Add ConfigurablePrivacyClassifier for operator-supplied patterns.
- PatternPrivacyClassifier defaults narrowed to hard PII only (SSN,
  credit card, credentials).
- Add force param to write_to_layer/append_to_layer to skip classifier.
- PrivacyClassifier trait returns SensitivityResult { is_sensitive,
  confidence } instead of bool, ready for probabilistic classifiers.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: remove redundant heartbeat match arm in memory_write

The heartbeat arm was identical to the catch-all — resolved_path
already points to paths::HEARTBEAT when target is "heartbeat".

Addresses review feedback from gemini-code-assist on #1112.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: return Result from PatternPrivacyClassifier::new()

Replace .expect() with proper error propagation per project
no-panics policy. Remove Default impl (unused in production).

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

* refactor: move memory_layers from GatewayConfig to WorkspaceConfig

Resolve merge conflicts between HEAD (transcription, search, env helpers)
and the workspace config branch. GatewayConfig no longer owns memory_layers;
WorkspaceConfig::resolve() handles parsing, validation (name length >64,
character set, empty scope, duplicates), and fallback defaults.

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

* test: strengthen privacy classifier and layer isolation coverage

Add 8 privacy classifier edge case tests (format variants, keywords,
longer documents, empty/partial inputs) and 5 layer write isolation
integration tests (cross-scope invisibility, overwrite, empty path,
sensitive-to-private no-redirect).

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

* fix: tautological test assertion and add WorkspaceConfig validation tests

Replace always-true `is_ok() || is_err()` in write_empty_path_to_layer
with actual behavior assertion (write succeeds with normalized empty path).

Add 8 unit tests for WorkspaceConfig::resolve() covering valid JSON parsing,
invalid JSON, empty/long/invalid-char layer names, empty scopes, duplicates,
and default fallback behavior.

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

* style: cargo fmt after staging merge

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

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>
Co-authored-by: [email protected] <[email protected]>

src/config/mod.rs

@@ -24,6 +24,7 @@ mod skills;
 mod transcription;
 mod tunnel;
 mod wasm;
+mod workspace;
 
 use std::collections::HashMap;
 use std::sync::{LazyLock, Mutex, Once};
@@ -53,6 +54,7 @@ pub use self::skills::SkillsConfig;
 pub use self::transcription::TranscriptionConfig;
 pub use self::tunnel::TunnelConfig;
 pub use self::wasm::WasmConfig;
+pub use self::workspace::WorkspaceConfig;
 pub use crate::llm::config::{
     BedrockConfig, CacheRetention, LlmConfig, NearAiConfig, OAUTH_PLACEHOLDER, OpenAiCodexConfig,
     RegistryProviderConfig,
@@ -98,6 +100,7 @@ pub struct Config {
     pub skills: SkillsConfig,
     pub transcription: TranscriptionConfig,
     pub search: WorkspaceSearchConfig,
+    pub workspace: WorkspaceConfig,
     pub observability: crate::observability::ObservabilityConfig,
     /// Channel-relay integration (Slack via external relay service).
     /// Present only when both `CHANNEL_RELAY_URL` and `CHANNEL_RELAY_API_KEY` are set.
@@ -175,6 +178,9 @@ impl Config {
             },
             transcription: TranscriptionConfig::default(),
             search: WorkspaceSearchConfig::default(),
+            workspace: WorkspaceConfig {
+                memory_layers: vec![],
+            },
             observability: crate::observability::ObservabilityConfig::default(),
             relay: None,
         }
@@ -305,13 +311,21 @@ impl Config {
     async fn build(settings: &Settings) -> Result<Self, ConfigError> {
         let owner_id = resolve_owner_id(settings)?;
 
+        let tunnel = TunnelConfig::resolve(settings)?;
+        let channels = ChannelsConfig::resolve(settings, &owner_id)?;
+        let workspace_user_id = channels
+            .gateway
+            .as_ref()
+            .map(|gw| gw.user_id.clone())
+            .unwrap_or_else(|| "default".to_string());
+
         Ok(Self {
             owner_id: owner_id.clone(),
             database: DatabaseConfig::resolve()?,
             llm: LlmConfig::resolve(settings)?,
             embeddings: EmbeddingsConfig::resolve(settings)?,
-            tunnel: TunnelConfig::resolve(settings)?,
-            channels: ChannelsConfig::resolve(settings, &owner_id)?,
+            tunnel,
+            channels,
             agent: AgentConfig::resolve(settings)?,
             safety: resolve_safety_config(settings)?,
             wasm: WasmConfig::resolve(settings)?,
@@ -325,6 +339,7 @@ impl Config {
             skills: SkillsConfig::resolve()?,
             transcription: TranscriptionConfig::resolve(settings)?,
             search: WorkspaceSearchConfig::resolve()?,
+            workspace: WorkspaceConfig::resolve(&workspace_user_id)?,
             observability: crate::observability::ObservabilityConfig {
                 backend: std::env::var("OBSERVABILITY_BACKEND").unwrap_or_else(|_| "none".into()),
             },