Detailed design: resolve four P1 cross-review findings

Apply repairs identified by the four-model cross-review (DeepSeek,
MIMO 2.5 Pro, GPT-5.5 Pro, Opus 4.8) and verify by regression:

- P1-01 Worker exit codes: align overview §11 and detailed-design §8.1
  with baselineV1 §8 (0 protocol-level completion / 1 uncaught exception
  / 2 startup or protocol error / 3 permission error / 4 parent cancelled
  / 5 hard timeout killed). Record that task outcomes are reported via
  WorkerResult.status, not exit codes.
- P1-02 PromptLayerLevel enum: add "safety" to interface-contracts §16
  so the enum fully covers prompt-layering-v1 §2 L0-L9 (plus
  system_debug applied within L9).
- P1-03 EventStore.project error handling: document in detailed-design
  §5.3 that a project() exception rolls back the full transaction,
  suppresses EventBus.publish(), returns AirError{kind:"system_error"},
  and triggers referential_check() on FK-off inconsistencies.
- P1-04 PromptLayerLoader completeness: record in detailed-design §10.2
  that PromptLayerLoader only owns L0/L1/L3/L5 while ContextAssembler
  composes L2/L4/L6/L7/L8/L9 from PermissionEngine, TaskSpec,
  SessionStore, and ToolRegistry sources; clarify runtime-role prompts.

Regression confirms baselineV1, overview, and detailed-design now share
identical exit code semantics, the PromptLayerLevel enum covers all ten
layers, EventStore error semantics are explicit, and the PromptLayer
loading responsibility split is fully documented.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AirPlan/docs/architecture/interface-contracts-v1.md

@@ -1019,16 +1019,17 @@ export interface ContextAssembler {
 }
 
 export type PromptLayerLevel =
-  | "runtime_invariant"
-  | "role"
-  | "project_rules"
-  | "task_spec"
-  | "architecture"
-  | "evidence"
-  | "tool_output"
-  | "conversation"
-  | "user_override"
-  | "system_debug"
+  | "runtime_invariant"  // L0
+  | "role"               // L1
+  | "safety"             // L2 (added to align with prompt-layering-v1 §2)
+  | "project_rules"      // L3
+  | "architecture"       // L4
+  | "task_spec"          // L5
+  | "evidence"           // L6
+  | "conversation"       // L7
+  | "tool_output"        // L8
+  | "user_override"      // L9
+  | "system_debug"       // (applied within L9 when present)
 
 export interface PromptLayer {
   level: PromptLayerLevel