feat(coder): orchestrator advanced flow patterns

- TriggerRule type (all_success/one_success/all_done) for parallel deps
- Variable substitution ($stepId.output.field) in agent step prompts
- Approval gate step kind (pauses flow via permission frames)
- flow_step_events table for append-only event-sourced step log
- evaluateTriggerRule pure function in flow-runner-decisions

apps/coder/src/conductor/types.ts

@@ -38,7 +38,9 @@ export interface StepContext {
   readonly model?: string;
 }
 
-export type StepKind = 'agent' | 'code';
+export type StepKind = 'agent' | 'code' | 'approval';
+
+export type TriggerRule = 'all_success' | 'one_success' | 'all_done';
 
 export interface Step {
   /** unique id within the flow; other steps depend on it by this id */
@@ -46,6 +48,8 @@ export interface Step {
   kind: StepKind;
   /** ids that must complete (or skip) before this step runs */
   deps?: string[];
+  /** how dependency satisfaction is evaluated (default: all_success) */
+  trigger_rule?: TriggerRule;
   /** for kind:'agent' — the persona file name under conductor/agents (no .md) */
   agent?: string;
   /**