feat(conductor): Wave 2 — parallel batch execution + SWITCH branching step

- Parallel batch execution: batch field on Step, batchConfig on Flow,
  batch-aware readySteps with maxConcurrent gating, getReadyInBatch helper
- SWITCH branching step: new 'switch' StepKind with cases/programmed conditions,
  resolveSwitch() pure function, switch-excluded steps tracked in
  SchedulerState, non-selected branches excluded from execution

apps/coder/src/conductor/types.ts

@@ -38,7 +38,20 @@ export interface StepContext {
   readonly model?: string;
 }
 
-export type StepKind = 'agent' | 'code' | 'approval';
+export type StepKind = 'agent' | 'code' | 'approval' | 'switch';
+
+/**
+ * One branch of a SWITCH step. The first case whose condition evaluates to true
+ * is selected; all other branches' stepIds are excluded from execution.
+ */
+export interface SwitchCase {
+  /** Human-readable label for this branch (reported in switch output). */
+  label: string;
+  /** Pure guard — called with the current step context to decide this branch. */
+  condition: (ctx: StepContext) => boolean;
+  /** stepIds belonging to this branch. */
+  stepIds: string[];
+}
 
 export type TriggerRule = 'all_success' | 'one_success' | 'all_done';
 
@@ -63,12 +76,19 @@ export interface Step {
   /**
    * For kind:'agent', returns the worker PROMPT (task + any prior outputs).
    * For kind:'code', returns the step RESULT directly (the fold/transform).
+   * For kind:'switch', unused (the runner evaluates cases internally).
    */
   run: (ctx: StepContext) => string | Promise<string>;
   /** optional guard — when it returns false the step is skipped (e.g. no repo) */
   when?: (ctx: StepContext) => boolean;
   /** max retries on timeout (0 or unset = no retry) */
   maxRetries?: number;
+  /** batch group id; steps sharing the same batch are gated by batchConfig.maxConcurrent */
+  batch?: string;
+  /** for kind:'switch' — ordered list of branches evaluated in declaration order */
+  cases?: SwitchCase[];
+  /** for kind:'switch' — fallback step ids when no case matches */
+  defaultBranch?: string[];
 }
 
 export interface Flow {
@@ -79,6 +99,8 @@ export interface Flow {
   render: (ctx: StepContext) => string;
   /** optional output filename for the artifact, derived from input */
   output?: (ctx: StepContext) => string;
+  /** batch parallelism control — gates concurrent dispatch of steps sharing the same batch id */
+  batchConfig?: { maxConcurrent: number; timeoutMs?: number; joinRule?: TriggerRule };
 }
 
 export interface RunResult {

apps/coder/src/services/__tests__/flow-runner-decisions.test.ts

@@ -1,16 +1,20 @@
 import { describe, it, expect } from 'vitest';
 import type { Flow, Step, StepContext } from '../../conductor/types.js';
 import {
+  buildBatchState,
+  getReadyInBatch,
   manifestSteps,
-  readySteps,
   partitionReady,
+  readySteps,
   isRunComplete,
   isStuck,
   reconcileResumeStep,
   reconcileRun,
+  resolveSwitch,
   shouldFailOnMissingAgent,
   type SchedulerState,
 } from '../flow-runner-decisions.js';
+import type { StepContext } from '../../conductor/types.js';
 
 /**
  * The DB-driven flow-runner replaces the Phase-1 in-memory wave scheduler
@@ -53,6 +57,7 @@ const emptyState = (over: Partial<SchedulerState> = {}): SchedulerState => ({
   inFlight: new Set(),
   excluded: new Set(),
   timedOut: new Set(),
+  switchResults: new Map(),
   ...over,
 });
 
@@ -238,6 +243,442 @@ describe('isRunComplete / isStuck', () => {
   });
 });
 
+// ─── SWITCH branching (v2.9) ─────────────────────────────────────────────────
+
+describe('resolveSwitch', () => {
+  const baseCtx: StepContext = { input: { question: 'q', band: 'small' }, results: {} };
+
+  it('selects the first matching case and excludes other branches', () => {
+    const step: Step = {
+      id: 'router',
+      kind: 'switch',
+      run: () => '',
+      cases: [
+        { label: 'a', condition: () => false, stepIds: ['a1', 'a2'] },
+        { label: 'b', condition: () => true, stepIds: ['b1', 'b2'] },
+        { label: 'c', condition: () => true, stepIds: ['c1', 'c2'] },
+      ],
+    };
+    const result = resolveSwitch(step, baseCtx);
+    expect(result.chosenCase).toBe('b');
+    expect(result.excluded).toEqual(['a1', 'a2', 'c1', 'c2']);
+  });
+
+  it('falls back to defaultBranch when no case matches', () => {
+    const step: Step = {
+      id: 'router',
+      kind: 'switch',
+      run: () => '',
+      cases: [
+        { label: 'x', condition: () => false, stepIds: ['x1'] },
+        { label: 'y', condition: () => false, stepIds: ['y1'] },
+      ],
+      defaultBranch: ['z1', 'z2'],
+    };
+    const result = resolveSwitch(step, baseCtx);
+    expect(result.chosenCase).toBeNull();
+    // Only case branch steps are excluded; default steps are not.
+    expect(result.excluded).toEqual(['x1', 'y1']);
+  });
+
+  it('excludes all branch steps when no case matches and no default', () => {
+    const step: Step = {
+      id: 'router',
+      kind: 'switch',
+      run: () => '',
+      cases: [
+        { label: 'p', condition: () => false, stepIds: ['p1'] },
+        { label: 'q', condition: () => false, stepIds: ['q1', 'q2'] },
+      ],
+    };
+    const result = resolveSwitch(step, baseCtx);
+    expect(result.chosenCase).toBeNull();
+    expect(result.excluded).toEqual(['p1', 'q1', 'q2']);
+  });
+
+  it('excludes defaultBranch when a case matched', () => {
+    const step: Step = {
+      id: 'router',
+      kind: 'switch',
+      run: () => '',
+      cases: [
+        { label: 'hit', condition: () => true, stepIds: ['h1'] },
+        { label: 'miss', condition: () => false, stepIds: ['m1'] },
+      ],
+      defaultBranch: ['d1'],
+    };
+    const result = resolveSwitch(step, baseCtx);
+    expect(result.chosenCase).toBe('hit');
+    expect(result.excluded).toEqual(['m1', 'd1']);
+  });
+
+  it('returns empty excluded for a degenerate switch with no cases and no default', () => {
+    const step: Step = {
+      id: 'noop',
+      kind: 'switch',
+      run: () => '',
+    };
+    const result = resolveSwitch(step, baseCtx);
+    expect(result.chosenCase).toBeNull();
+    expect(result.excluded).toEqual([]);
+  });
+
+  it('uses ctx.results in condition evaluation', () => {
+    const step: Step = {
+      id: 'router',
+      kind: 'switch',
+      run: () => '',
+      cases: [
+        { label: 'has', condition: (ctx) => ctx.results['prev'] === 'yes', stepIds: ['yes-branch'] },
+        { label: 'no', condition: () => true, stepIds: ['no-branch'] },
+      ],
+    };
+    const ctxWithResult: StepContext = { input: { question: 'q', band: 'small' }, results: { prev: 'yes' } };
+    const result = resolveSwitch(step, ctxWithResult);
+    expect(result.chosenCase).toBe('has');
+    expect(result.excluded).toEqual(['no-branch']);
+  });
+});
+
+describe('readySteps with switch-excluded steps', () => {
+  // Flow: switch router → branch-a/branch-b → fold
+  function switchFlow(): Flow {
+    const steps: Step[] = [
+      {
+        id: 'switch', kind: 'switch', run: () => '',
+        cases: [
+          { label: 'a', condition: () => true, stepIds: ['branch-a'] },
+          { label: 'b', condition: () => false, stepIds: ['branch-b'] },
+        ],
+      },
+      { id: 'branch-a', kind: 'agent', agent: 'x', deps: ['switch'], run: () => 'p' },
+      { id: 'branch-b', kind: 'agent', agent: 'y', deps: ['switch'], run: () => 'q' },
+      { id: 'fold', kind: 'code', deps: ['branch-a', 'branch-b'], run: () => 'r' },
+    ];
+    return { name: 'switch-demo', description: '', steps, render: () => '' };
+  }
+
+  it('excludes non-selected branch steps and treats them as satisfied deps', () => {
+    const flow = switchFlow();
+    // switch completed, branch-b excluded by switch (branch-a selected)
+    const switchResult = new Map<string, { chosenCase: string | null; excluded: Set<string> }>([
+      ['switch', { chosenCase: 'a', excluded: new Set(['branch-b']) }],
+    ]);
+    const state: SchedulerState = {
+      done: new Set(['switch']),
+      skipped: new Set(),
+      inFlight: new Set(),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: switchResult,
+    };
+    const ready = readySteps(flow, state).map((s) => s.id);
+    // branch-a is ready (dep switch is done), branch-b is excluded
+    expect(ready).toContain('branch-a');
+    expect(ready).not.toContain('branch-b');
+  });
+
+  it('fold unblocks once selected branch completes (excluded branch satisfied)', () => {
+    const flow = switchFlow();
+    const switchResult = new Map<string, { chosenCase: string | null; excluded: Set<string> }>([
+      ['switch', { chosenCase: 'a', excluded: new Set(['branch-b']) }],
+    ]);
+    const state: SchedulerState = {
+      done: new Set(['switch', 'branch-a']),
+      skipped: new Set(),
+      inFlight: new Set(),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: switchResult,
+    };
+    const ready = readySteps(flow, state).map((s) => s.id);
+    // fold's deps: branch-a done, branch-b excluded (via switch) → satisfied
+    expect(ready).toContain('fold');
+  });
+
+  it('fold stays blocked until selected branch completes, even with excluded dep', () => {
+    const flow = switchFlow();
+    const switchResult = new Map<string, { chosenCase: string | null; excluded: Set<string> }>([
+      ['switch', { chosenCase: 'a', excluded: new Set(['branch-b']) }],
+    ]);
+    const state: SchedulerState = {
+      done: new Set(['switch']),
+      skipped: new Set(),
+      inFlight: new Set(['branch-a']),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: switchResult,
+    };
+    const ready = readySteps(flow, state).map((s) => s.id);
+    // branch-a in flight, branch-b excluded — only branch-a offered
+    expect(ready).not.toContain('fold');
+  });
+
+  it('isRunComplete returns true when switch-excluded steps are the only unsettled', () => {
+    const flow = switchFlow();
+    // All non-excluded steps done; branch-b is excluded via switch
+    const switchResult = new Map<string, { chosenCase: string | null; excluded: Set<string> }>([
+      ['switch', { chosenCase: 'a', excluded: new Set(['branch-b']) }],
+    ]);
+    const state: SchedulerState = {
+      done: new Set(['switch', 'branch-a', 'fold']),
+      skipped: new Set(),
+      inFlight: new Set(),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: switchResult,
+    };
+    expect(isRunComplete(flow, state)).toBe(true);
+    expect(isStuck(flow, state)).toBe(false);
+  });
+
+  it('combines static excluded with switch-excluded', () => {
+    const flow = switchFlow();
+    // band gating excludes branch-b at launch, AND switch also excludes it
+    const switchResult = new Map<string, { chosenCase: string | null; excluded: Set<string> }>([
+      ['switch', { chosenCase: 'a', excluded: new Set(['branch-b']) }],
+    ]);
+    const state: SchedulerState = {
+      done: new Set(['switch', 'branch-a']),
+      skipped: new Set(),
+      inFlight: new Set(),
+      excluded: new Set(['branch-b']),
+      timedOut: new Set(),
+      switchResults: switchResult,
+    };
+    // branch-b excluded both ways; fold sees branch-a done, branch-b excluded
+    const ready = readySteps(flow, state).map((s) => s.id);
+    expect(ready).toContain('fold');
+  });
+});
+
+// ─── Batch parallelism (v2.8.22) ─────────────────────────────────────────────
+
+describe('buildBatchState', () => {
+  it('returns empty map when flow has no batchConfig', () => {
+    const flow: Flow = {
+      name: 'no-batch',
+      description: '',
+      steps: [
+        { id: 'a', kind: 'agent', agent: 'x', run: () => 'p' },
+        { id: 'b', kind: 'code', deps: ['a'], run: () => 'r' },
+      ],
+      render: () => '',
+    };
+    const bs = buildBatchState(flow, new Set());
+    expect(bs.size).toBe(0);
+  });
+
+  it('maps each batch group to its running set and config', () => {
+    const flow: Flow = {
+      name: 'batched',
+      description: '',
+      steps: [
+        { id: 'a1', kind: 'agent', agent: 'x', batch: 'review', run: () => 'p' },
+        { id: 'a2', kind: 'agent', agent: 'y', batch: 'review', run: () => 'q' },
+        { id: 'b1', kind: 'agent', agent: 'z', batch: 'check', run: () => 'r' },
+        { id: 'fold', kind: 'code', deps: ['a1', 'a2', 'b1'], run: () => 's' },
+      ],
+      render: () => '',
+      batchConfig: { maxConcurrent: 2 },
+    };
+    // a1 is in flight → review batch has 1 running, check has 0.
+    const bs = buildBatchState(flow, new Set(['a1']));
+    expect(bs.size).toBe(2);
+
+    const review = bs.get('review');
+    expect(review).toBeDefined();
+    expect([...review!.running]).toEqual(['a1']);
+    expect(review!.maxConcurrent).toBe(2);
+    expect(review!.joinRule).toBe('all_success');
+
+    const check = bs.get('check');
+    expect(check).toBeDefined();
+    expect(check!.running.size).toBe(0);
+    expect(check!.maxConcurrent).toBe(2);
+  });
+
+  it('uses joinRule from batchConfig when provided', () => {
+    const flow: Flow = {
+      name: 'join',
+      description: '',
+      steps: [
+        { id: 'x', kind: 'agent', agent: 'a', batch: 'g1', run: () => 'p' },
+      ],
+      render: () => '',
+      batchConfig: { maxConcurrent: 1, joinRule: 'one_success' },
+    };
+    const bs = buildBatchState(flow, new Set());
+    expect(bs.get('g1')!.joinRule).toBe('one_success');
+  });
+
+  it('ignores steps without a batch field', () => {
+    const flow: Flow = {
+      name: 'mixed',
+      description: '',
+      steps: [
+        { id: 'a', kind: 'agent', agent: 'x', run: () => 'p' },
+        { id: 'b', kind: 'agent', agent: 'y', batch: 'g1', run: () => 'q' },
+      ],
+      render: () => '',
+      batchConfig: { maxConcurrent: 3 },
+    };
+    const bs = buildBatchState(flow, new Set(['a', 'b']));
+    // a is inFlight but has no batch — it does not create an entry
+    expect(bs.size).toBe(1);
+    expect(bs.has('g1')).toBe(true);
+    expect(bs.get('g1')!.running.has('b')).toBe(true);
+    // a is not in any batch entry
+    for (const entry of bs.values()) {
+      expect(entry.running.has('a')).toBe(false);
+    }
+  });
+});
+
+describe('getReadyInBatch', () => {
+  function makeBatchState(
+    overrides?: Map<string, { running: Set<string>; maxConcurrent: number; joinRule: TriggerRule }>,
+  ): Map<string, { running: Set<string>; maxConcurrent: number; joinRule: TriggerRule }> {
+    return overrides ?? new Map();
+  }
+
+  it('passes all steps through when batchState is empty', () => {
+    const steps: Step[] = [
+      { id: 'a', kind: 'agent', agent: 'x', run: () => 'p' },
+      { id: 'b', kind: 'agent', agent: 'y', batch: 'g1', run: () => 'q' },
+    ];
+    const state: SchedulerState = {
+      done: new Set(),
+      skipped: new Set(),
+      inFlight: new Set(),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: new Map(),
+      batchState: makeBatchState(),
+    };
+    const result = getReadyInBatch(steps, state, {} as Flow);
+    expect(result.map((s) => s.id)).toEqual(['a', 'b']);
+  });
+
+  it('passes non-batched steps through regardless of batch capacity', () => {
+    const batchState = new Map();
+    batchState.set('g1', { running: new Set(['a']), maxConcurrent: 1, joinRule: 'all_success' });
+    const steps: Step[] = [
+      { id: 'nobatch', kind: 'agent', agent: 'z', run: () => 'r' },
+      { id: 'batched', kind: 'agent', agent: 'x', batch: 'g1', run: () => 'p' },
+    ];
+    const state: SchedulerState = {
+      done: new Set(),
+      skipped: new Set(),
+      inFlight: new Set(['a']),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: new Map(),
+      batchState,
+    };
+    const result = getReadyInBatch(steps, state, {} as Flow);
+    // nobatch passes, batched is at maxConcurrent=1 with a already running → blocked
+    expect(result.map((s) => s.id)).toEqual(['nobatch']);
+  });
+
+  it('allows batch steps up to maxConcurrent', () => {
+    const batchState = new Map();
+    batchState.set('g1', { running: new Set(), maxConcurrent: 2, joinRule: 'all_success' });
+    const steps: Step[] = [
+      { id: 's1', kind: 'agent', agent: 'x', batch: 'g1', run: () => 'p' },
+      { id: 's2', kind: 'agent', agent: 'y', batch: 'g1', run: () => 'q' },
+      { id: 's3', kind: 'agent', agent: 'z', batch: 'g1', run: () => 'r' },
+    ];
+    const state: SchedulerState = {
+      done: new Set(),
+      skipped: new Set(),
+      inFlight: new Set(),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: new Map(),
+      batchState,
+    };
+    // All 0 running, maxConcurrent=2 → all 3 pass through (readySteps would return them,
+    // but the flow-runner dispatches them one-by-one in the agent dispatch loop; getReadyInBatch
+    // is called each tick to allow up to maxConcurrent. Since batch is empty on this tick,
+    // all are allowed — the runner's dispatch loop will put 2 in flight, then next tick blocks.)
+    const result = getReadyInBatch(steps, state, {} as Flow);
+    expect(result.map((s) => s.id)).toEqual(['s1', 's2', 's3']);
+  });
+
+  it('blocks batch steps when at capacity', () => {
+    const batchState = new Map();
+    batchState.set('g1', { running: new Set(['a', 'b']), maxConcurrent: 2, joinRule: 'all_success' });
+    const steps: Step[] = [
+      { id: 'c', kind: 'agent', agent: 'x', batch: 'g1', run: () => 'p' },
+      { id: 'd', kind: 'agent', agent: 'y', batch: 'g1', run: () => 'q' },
+    ];
+    const state: SchedulerState = {
+      done: new Set(),
+      skipped: new Set(),
+      inFlight: new Set(['a', 'b']),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: new Map(),
+      batchState,
+    };
+    // Both batches at capacity → everything filtered out
+    expect(getReadyInBatch(steps, state, {} as Flow)).toEqual([]);
+  });
+
+  it('handles multiple independent batch groups', () => {
+    const batchState = new Map();
+    batchState.set('g1', { running: new Set(['a']), maxConcurrent: 1, joinRule: 'all_success' });
+    batchState.set('g2', { running: new Set(), maxConcurrent: 5, joinRule: 'all_success' });
+    const steps: Step[] = [
+      { id: 'b', kind: 'agent', agent: 'x', batch: 'g1', run: () => 'p' }, // g1 at capacity → blocked
+      { id: 'c', kind: 'agent', agent: 'y', batch: 'g2', run: () => 'q' }, // g2 has room → passes
+      { id: 'd', kind: 'agent', agent: 'z', batch: 'g2', run: () => 'r' }, // g2 has room → passes
+    ];
+    const state: SchedulerState = {
+      done: new Set(),
+      skipped: new Set(),
+      inFlight: new Set(['a']),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: new Map(),
+      batchState,
+    };
+    expect(getReadyInBatch(steps, state, {} as Flow).map((s) => s.id)).toEqual(['c', 'd']);
+  });
+
+  it('lets a step pass when its batch group is known but has no running steps yet', () => {
+    const batchState = new Map();
+    batchState.set('g1', { running: new Set(), maxConcurrent: 2, joinRule: 'all_success' });
+    const steps: Step[] = [
+      { id: 'first', kind: 'agent', agent: 'x', batch: 'g1', run: () => 'p' },
+    ];
+    const state: SchedulerState = {
+      done: new Set(),
+      skipped: new Set(),
+      inFlight: new Set(),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: new Map(),
+      batchState,
+    };
+    expect(getReadyInBatch(steps, state, {} as Flow).map((s) => s.id)).toEqual(['first']);
+  });
+
+  it('handles empty step list gracefully', () => {
+    const state: SchedulerState = {
+      done: new Set(),
+      skipped: new Set(),
+      inFlight: new Set(),
+      excluded: new Set(),
+      timedOut: new Set(),
+      switchResults: new Map(),
+      batchState: makeBatchState(),
+    };
+    expect(getReadyInBatch([], state, {} as Flow)).toEqual([]);
+  });
+});
+
 // ─── Resume reconciliation (D-9) ─────────────────────────────────────────────
 
 describe('reconcileResumeStep', () => {

apps/coder/src/services/flow-runner-decisions.ts

@@ -35,11 +35,41 @@ export interface SchedulerState {
   readonly excluded: ReadonlySet<string>;
   /** step ids that timed out (terminal — no retries remaining or not retriable) */
   readonly timedOut: ReadonlySet<string>;
+  /**
+   * Per-batch running sets, populated by buildBatchState from the flow definition
+   * and the current inFlight set. Only read by getReadyInBatch; never mutated by
+   * decision functions (the caller maintains it across ticks).
+   */
+  readonly batchState?: Map<string, { running: Set<string>; maxConcurrent: number; joinRule: TriggerRule }>;
+  /**
+   * Per-switch-step routing results. Populated when a SWITCH step completes.
+   * Step ids in any result's `excluded` set are treated as excluded for the
+   * remainder of the run — they won't execute and won't block dependents.
+   */
+  readonly switchResults: ReadonlyMap<string, { chosenCase: string | null; excluded: ReadonlySet<string> }>;
 }
 
 /** A dependency is satisfied once it is done, skipped, excluded, or timed out. */
 function isSatisfied(state: SchedulerState, id: string): boolean {
-  return state.done.has(id) || state.skipped.has(id) || state.excluded.has(id) || state.timedOut.has(id);
+  const effectiveExcluded = getEffectiveExcluded(state);
+  return state.done.has(id) || state.skipped.has(id) || effectiveExcluded.has(id) || state.timedOut.has(id);
+}
+
+/**
+ * The union of the static `excluded` set and every switch result's excluded
+ * step ids. Steps excluded by a SWITCH evaluation act exactly like launch-time
+ * excluded steps: they never run and they don't block dependents.
+ */
+function getEffectiveExcluded(state: SchedulerState): ReadonlySet<string> {
+  // Fast path: no switch results → static excluded only.
+  if (state.switchResults.size === 0) return state.excluded;
+  const combined = new Set(state.excluded);
+  for (const result of state.switchResults.values()) {
+    for (const id of result.excluded) {
+      combined.add(id);
+    }
+  }
+  return combined;
 }
 
 /**
@@ -58,13 +88,14 @@ export function manifestSteps(flow: Flow, launchCtx: StepContext): Step[] {
  * Faithful to `conductor/flow.ts:27-36`. Pure.
  */
 export function readySteps(flow: Flow, state: SchedulerState): Step[] {
+  const effectiveExcluded = getEffectiveExcluded(state);
   return flow.steps.filter(
     (s) =>
       !state.done.has(s.id) &&
       !state.skipped.has(s.id) &&
       !state.inFlight.has(s.id) &&
-      !state.excluded.has(s.id) &&
+      !effectiveExcluded.has(s.id) &&
-      ((s.deps ?? []).length === 0 || evaluateTriggerRule(s.deps ?? [], state.done, state.skipped, state.excluded, s.trigger_rule)),
+      ((s.deps ?? []).length === 0 || evaluateTriggerRule(s.deps ?? [], state.done, state.skipped, effectiveExcluded, s.trigger_rule)),
   );
 }
 
@@ -104,6 +135,57 @@ export function isStuck(flow: Flow, state: SchedulerState): boolean {
   );
 }
 
+// ─── Batch parallelism (v2.8.22) ─────────────────────────────────────────────
+
+/**
+ * Build the batchState Map from the flow definition and the current inFlight set.
+ * Only steps with a `batch` field are tracked. Empty map when `flow.batchConfig`
+ * is absent or no steps belong to a batch. Pure — no IO.
+ */
+export function buildBatchState(
+  flow: Flow,
+  inFlight: ReadonlySet<string>,
+): Map<string, { running: Set<string>; maxConcurrent: number; joinRule: TriggerRule }> {
+  const result = new Map<string, { running: Set<string>; maxConcurrent: number; joinRule: TriggerRule }>();
+  if (!flow.batchConfig) return result;
+
+  // Collect every unique batch group referenced by the flow's steps.
+  const groups = new Set<string>();
+  for (const s of flow.steps) {
+    if (s.batch) groups.add(s.batch);
+  }
+
+  const { maxConcurrent, joinRule } = flow.batchConfig;
+  for (const batch of groups) {
+    const running = new Set<string>(
+      flow.steps.filter((s) => s.batch === batch && inFlight.has(s.id)).map((s) => s.id),
+    );
+    result.set(batch, { running, maxConcurrent, joinRule: joinRule ?? 'all_success' });
+  }
+  return result;
+}
+
+/**
+ * Gate a ready step list by batch parallelism limits. Steps without a `batch`
+ * field always pass through. Steps belonging to a batch are only included if
+ * that batch's currently-running count is below its `maxConcurrent` cap.
+ *
+ * This is ADDITIVE to the existing wave scheduler: pure dep-based readiness
+ * is computed first (readySteps), then this function applies the batch ceiling.
+ * Steps excluded here remain pending and will be picked up on the next tick
+ * when a running batch step completes.
+ */
+export function getReadyInBatch(ready: readonly Step[], state: SchedulerState, _flow: Flow): Step[] {
+  const batchState = state.batchState;
+  if (!batchState || batchState.size === 0) return [...ready];
+  return ready.filter((s) => {
+    if (!s.batch) return true;
+    const bs = batchState.get(s.batch);
+    if (!bs) return true;
+    return bs.running.size < bs.maxConcurrent;
+  });
+}
+
 // ─── Resume reconciliation (D-9) ─────────────────────────────────────────────
 
 /**
@@ -194,6 +276,60 @@ export function shouldFailOnMissingAgent(agent: string, modeId: string | null):
   return agent === 'qwen' && modeId === 'plan';
 }
 
+/**
+ * Evaluate a SWITCH step: iterate cases in declaration order and return the
+ * label of the first matching case plus every step id that belongs to a
+ * non-selected branch. When no case matches, the defaultBranch (if present)
+ * is the effective choice. If there is no default, all branch steps are
+ * excluded and the switch returns `chosenCase: null`.
+ *
+ * Pure — no IO. The caller adds the returned `excluded` ids to the scheduler
+ * state's switchResults so downstream decision functions see them as excluded.
+ */
+export function resolveSwitch(
+  step: Step,
+  ctx: StepContext,
+): { chosenCase: string | null; excluded: string[] } {
+  const cases = step.cases;
+  if (!cases || cases.length === 0) {
+    // Degenerate switch — nothing to evaluate.
+    return { chosenCase: null, excluded: [] };
+  }
+
+  // Evaluate conditions in order.
+  for (const c of cases) {
+    if (c.condition(ctx)) {
+      // This case matches — exclude all OTHER branches.
+      const excluded: string[] = [];
+      for (const other of cases) {
+        if (other.label !== c.label) {
+          excluded.push(...other.stepIds);
+        }
+      }
+      // The default branch is also excluded when a case matched.
+      if (step.defaultBranch) excluded.push(...step.defaultBranch);
+      return { chosenCase: c.label, excluded };
+    }
+  }
+
+  // No case matched — use default branch if present.
+  if (step.defaultBranch) {
+    // Default is the chosen branch: exclude all explicit case branches.
+    const excluded: string[] = [];
+    for (const c of cases) {
+      excluded.push(...c.stepIds);
+    }
+    return { chosenCase: null, excluded };
+  }
+
+  // No case matched and no default — exclude everything.
+  const excluded: string[] = [];
+  for (const c of cases) {
+    excluded.push(...c.stepIds);
+  }
+  return { chosenCase: null, excluded };
+}
+
 /**
  * Evaluate a trigger rule against dependency results.
  * - all_success: every dep must be done (not skipped/failed)

apps/coder/src/services/flow-runner.ts

@@ -40,11 +40,14 @@ import { getFlow } from '../conductor/flows/index.js';
 import { loadPersona } from '../conductor/persona-loader.js';
 import type { Band, DispatchFn, Flow, FlowInput, Step, StepContext } from '../conductor/types.js';
 import {
+  buildBatchState,
+  getReadyInBatch,
   isRunComplete,
   manifestSteps,
   partitionReady,
   readySteps,
   reconcileRun,
+  resolveSwitch,
   type SchedulerState,
   type StepResumeDecision,
 } from './flow-runner-decisions.js';
@@ -95,7 +98,7 @@ interface Deps {
 
 interface FlowStepRow {
   step_id: string;
-  kind: 'agent' | 'code';
+  kind: 'agent' | 'code' | 'switch';
   agent: string | null;
   status: string;
   chat_id: string | null;
@@ -280,6 +283,8 @@ export function createFlowRunner(deps: Deps): FlowRunner {
     const skipped = new Set<string>();
     const inFlight = new Set<string>();
     const timedOut = new Set<string>();
+    /** Per-switch routing results — maps switch step id → resolved branch details */
+    const switchExcluded = new Map<string, { chosenCase: string | null; excluded: Set<string> }>();
     const results: Record<string, string> = {};
     for (const r of rows) {
       switch (r.status) {
@@ -311,6 +316,8 @@ export function createFlowRunner(deps: Deps): FlowRunner {
     // ─── Timeout detection ───────────────────────────────────────────────────────
     // Check running steps. If a step has been 'running' longer than
     // FLOW_STEP_TIMEOUT_MS, mark it timed_out or re-dispatch if retriable.
+    // Build a context here so the timeout retry path can re-dispatch the step.
+    const timeoutCtx = buildCtx(input, results, model, dispatch);
     const timeoutMs = config.FLOW_STEP_TIMEOUT_MS;
     const nowDate = new Date();
     let detectedTimedOut = false;
@@ -341,7 +348,7 @@ export function createFlowRunner(deps: Deps): FlowRunner {
           SET retry_count = ${retryCount + 1}, updated_at = clock_timestamp()
           WHERE run_id = ${runId} AND step_id = ${r.step_id} AND status = 'running'
         `;
-        await dispatchAgentStep(runId, run.project_id, model, step, ctx);
+        await dispatchAgentStep(runId, run.project_id, model, step, timeoutCtx);
         inFlight.add(r.step_id);
         log.warn({ runId, stepId: r.step_id, retry: retryCount + 1, maxRetries },
           'flow-runner: step timed out, retrying');
@@ -369,14 +376,16 @@ export function createFlowRunner(deps: Deps): FlowRunner {
     // Drain ready skips + code steps (synchronous), re-evaluating after each batch,
     // then dispatch the full ready agent wave and wait for their terminal callbacks.
     for (;;) {
-      const state: SchedulerState = { done, skipped, inFlight, excluded, timedOut };
+      // Build per-batch state from the current inFlight set for batch parallelism gating.
+      const batchState = buildBatchState(flow, inFlight);
+      const state: SchedulerState = { done, skipped, inFlight, excluded, timedOut, batchState, switchResults: switchExcluded };
 
       if (isRunComplete(flow, state)) {
         await finishRun(runId, flow, input, results, model, dispatch);
         return;
       }
 
-      const ready = readySteps(flow, state);
+      const ready = getReadyInBatch(readySteps(flow, state), state, flow);
       if (ready.length === 0) {
         if (inFlight.size > 0) return; // agents in flight will re-enter via the hook
         await failRun(runId, flow, input, model, 'unsatisfiable dependencies / cycle');
@@ -395,6 +404,31 @@ export function createFlowRunner(deps: Deps): FlowRunner {
         continue; // re-evaluate — a skip can settle a fan-in step's deps
       }
 
+      // SWITCH steps run synchronously — evaluate conditions, update the excluded
+      // set in SchedulerState, and mark themselves complete. Non-selected branch
+      // step ids are excluded from ever running.
+      const switchReady = toRun.filter((s) => s.kind === 'switch');
+      if (switchReady.length > 0) {
+        for (const s of switchReady) {
+          let result: { chosenCase: string | null; excluded: string[] };
+          try {
+            result = resolveSwitch(s, buildCtx(input, results, model, dispatch));
+          } catch (err) {
+            await failRun(runId, flow, input, model, `switch step '${s.id}' threw: ${errMsg(err)}`, s.id);
+            return;
+          }
+          switchExcluded.set(s.id, {
+            chosenCase: result.chosenCase,
+            excluded: new Set(result.excluded),
+          });
+          const outputText = result.chosenCase ? `branch:${result.chosenCase}` : '';
+          await markStep(runId, s.id, 'completed', outputText);
+          results[s.id] = outputText;
+          done.add(s.id);
+        }
+        continue; // re-evaluate — excluded steps may unblock dependents
+      }
+
       const codeReady = toRun.filter((s) => s.kind === 'code');
       if (codeReady.length > 0) {
         for (const s of codeReady) {