feat: complete multi-tenant isolation — phases 2–4 (#1614)

* feat: complete multi-tenant isolation — per-user budgets, model selection, heartbeat cycling

Finishes the remaining isolation work from phases 2–4 of #59:

Phase 2 (DB scoping): Fix /status and /list commands to use _for_user
DB variants instead of global queries that leaked cross-user job data.

Phase 3 (Runtime isolation): Per-user workspace in routine engine's
spawn_fire so lightweight routines run in the correct user context.
Per-user daily cost tracking in CostGuard with configurable budget via
MAX_COST_PER_USER_PER_DAY_CENTS. Multi-user heartbeat that cycles
through all users with routines, auto-detected from GATEWAY_USER_TOKENS.

Phase 4 (Provider/tools): Per-user model selection via preferred_model
setting — looked up from SettingsStore on first iteration, threaded
through ReasoningContext.model_override to CompletionRequest. Works
with providers that support per-request model overrides (NearAI).

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

* fix: use selected_model setting key to match /model command persistence

The dispatcher was reading "preferred_model" but the /model command
(merged from staging) persists to "selected_model". Since set_setting
is already per-user scoped, using the same key makes /model work as
the per-user model override in multi-tenant mode.

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

* fix: heartbeat hygiene, /model multi-tenant guard, RigAdapter model override

Three follow-up fixes for multi-tenant isolation:

1. Multi-user heartbeat now runs memory hygiene per user before each
   heartbeat check, matching single-user heartbeat behavior.

2. /model command in multi-tenant mode only persists to per-user
   settings (selected_model) without calling set_model() on the shared
   LlmProvider. The per-request model_override in the dispatcher reads
   from the same setting. Added multi_tenant flag to AgentConfig
   (auto-detected from GATEWAY_USER_TOKENS).

3. RigAdapter now supports per-request model overrides by injecting the
   model name into rig-core's additional_params. OpenAI/Anthropic/Ollama
   API servers use last-key-wins for duplicate JSON keys, so the override
   takes effect via serde's flatten serialization order.

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

* fix: address PR review — cost model attribution, heartbeat concurrency, pruning

Fixes from review comments on #1614:

- Cost tracking now uses the override model name (not active_model_name)
  when a per-user model override is active, for accurate attribution.
- Multi-user heartbeat runs per-user checks concurrently via JoinSet
  instead of sequentially, preventing one slow user from blocking others.
- Per-user failure counts tracked independently; users exceeding
  max_failures are skipped (matching single-user semantics).
- per_user_daily_cost HashMap pruned on day rollover to prevent
  unbounded growth in long-lived deployments.
- Doc comment fixed: says "routines" not "active routines".

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

* fix: /status ownership, model persistence scoping, heartbeat robustness

Addresses second round of PR review on #1614:

- /status <job_id> DB path now validates job.user_id == requesting user
  before returning data (was missing ownership check, security fix).

- persist_selected_model takes user_id param instead of owner_id, and
  skips .env/TOML writes in multi-tenant mode (these are shared global
  files). handle_system_command now receives user_id from caller.

- JoinSet collection handles Err(JoinError) explicitly instead of
  silently dropping panicked tasks.

- Notification forwarder extracts owner_id from response metadata in
  multi-tenant mode for per-user routing instead of broadcasting to
  the agent owner.

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

* fix: cost pricing, fire_manual workspace, heartbeat concurrency cap

Round 3 review fixes:

- Cost tracking passes None for cost_per_token when model override is
  active, letting CostGuard look up pricing by model name instead of
  using the default provider's rates (serrrfirat).

- fire_manual() now uses per-user workspace, matching spawn_fire()
  pattern (serrrfirat).

- Removed MULTI_TENANT env var — multi-tenant mode is auto-detected
  solely from GATEWAY_USER_TOKENS presence (serrrfirat + Copilot).

- Multi-user heartbeat capped at 8 concurrent tasks to avoid flooding
  the LLM provider (serrrfirat + Copilot).

- Fixed inject_model_override doc comment accuracy (Copilot).

- Added comment explaining multi-tenant notification routing priority
  (Copilot).

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

* feat: user-scoped webhook endpoint for multi-tenant isolation

Adds POST /api/webhooks/u/{user_id}/{path} — a user-scoped webhook
endpoint that filters the routine lookup by user_id, preventing
cross-user webhook triggering when paths collide.

The existing /api/webhooks/{path} endpoint remains unchanged for
backward compatibility in single-user deployments.

Changes:
- get_webhook_routine_by_path gains user_id: Option<&str> param
- Both postgres and libsql implementations add AND user_id = ? filter
  when user_id is provided
- New webhook_trigger_user_scoped_handler extracts (user_id, path)
  from URL and passes to shared fire_webhook_inner logic
- Route registered on public router (webhooks are called by external
  services that can't send bearer tokens)

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

* feat: add TenantCtx for compile-time tenant isolation

Implements zmanian's architectural proposal from #1614 review:
two-tier scoped database access (TenantScope/AdminScope) so handler
code cannot accidentally bypass tenant scoping.

TenantScope (default): wraps user_id + Arc<dyn Database>, auto-binds
user_id on every operation. ID-based lookups return None for cross-
tenant resources. No escape hatch — forgetting to scope is a compile
error.

AdminScope (explicit opt-in): cross-tenant access for system-level
components (heartbeat, routine engine, self-repair, scheduler, worker).

TenantCtx bundles TenantScope + workspace + cost guard + per-user
rate limiting. Constructed once per request in handle_message, threaded
through all command handlers and ChatDelegate.

Key changes:
- New src/tenant.rs (~920 lines): TenantScope, AdminScope, TenantCtx,
  TenantRateState, TenantRateRegistry
- All command handlers: user_id: &str → ctx: &TenantCtx
- ChatDelegate: cost check/record/settings via self.tenant
- System components: store field changed to AdminScope
- Config: TENANT_MAX_LLM_CONCURRENT, TENANT_MAX_JOBS_CONCURRENT env vars
- Fixes bug: /status <job_id> cross-tenant leak (now auto-filtered)

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

---------

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

src/worker/job.rs

@@ -20,7 +20,6 @@ use crate::agent::scheduler::WorkerMessage;
 use crate::agent::task::TaskOutput;
 use crate::channels::web::types::ToolDecisionDto;
 use crate::context::{ContextManager, JobState};
-use crate::db::Database;
 use crate::error::Error;
 use crate::hooks::HookRegistry;
 use crate::llm::{
@@ -28,6 +27,7 @@ use crate::llm::{
     ToolSelection,
 };
 use crate::safety::SafetyLayer;
+use crate::tenant::AdminScope;
 use crate::tools::execute::process_tool_result;
 use crate::tools::rate_limiter::RateLimitResult;
 use crate::tools::{
@@ -45,7 +45,7 @@ pub struct WorkerDeps {
     pub llm: Arc<dyn LlmProvider>,
     pub safety: Arc<SafetyLayer>,
     pub tools: Arc<ToolRegistry>,
-    pub store: Option<Arc<dyn Database>>,
+    pub store: Option<AdminScope>,
     pub hooks: Arc<HookRegistry>,
     pub timeout: Duration,
     pub use_planning: bool,
@@ -94,7 +94,7 @@ impl Worker {
         &self.deps.tools
     }
 
-    fn store(&self) -> Option<&Arc<dyn Database>> {
+    fn store(&self) -> Option<&AdminScope> {
         self.deps.store.as_ref()
     }