diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index eabab69..c7bb25a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 15
     env:
-      PY_FIXTURE_REF: 6cedcd955fcf4b4e687ea85771ebbc5302e5fe01
+      PY_FIXTURE_REF: caf37689ee6c1c99ddf0067f6486daf6cc9bb0ed
       PY_FIXTURE_CHECKOUT: /tmp/context-compiler-source
 
     steps:
diff --git a/README.md b/README.md
index 0e8a7bb..9e8fc15 100644
--- a/README.md
+++ b/README.md
@@ -120,9 +120,14 @@ State snapshots are intentionally opaque. Prefer helpers such as
 - `getPremiseValue(state)` / `getPolicyItems(state, value?)` -> read helpers for state.
 - `step(engine, input)` -> controller step envelope (`output_version`, `mode`, `decision`, `state`).
 - `preview(engine, input)` -> dry-run step envelope with `state_before`, `state_after`, `diff`, and `would_mutate` (live engine state is restored).
+- `getStepDecision(stepResult)` / `getStepState(stepResult)` -> read helpers for controller step results.
+- `getPreviewDecision(previewResult)` / `getPreviewStateAfter(previewResult)` / `previewWouldMutate(previewResult)` -> read helpers for controller preview results.
+- `diffHasChanges(diff)` -> read helper for the structural diff `changed` flag.
 - `stateDiff(before, after)` -> structural state diff used by preview.
 - `DECISION_PASSTHROUGH` / `DECISION_UPDATE` / `DECISION_CLARIFY` -> decision kind constants.
 
+Prefer the controller helper accessors over direct controller result property reads in TypeScript examples and app code.
+
 ## Experimental Preprocessor
 
 The preprocessor is an optional host-side layer that can recognize some
@@ -141,7 +146,12 @@ Safety guidance:
 Experimental preprocessor APIs are available via package subpath:
 
 ```ts
-import { preprocessHeuristic, parsePreprocessorOutput, validatePreprocessorOutput } from '@rlippmann/context-compiler/experimental/preprocessor';
+import {
+  PREPROCESS_OUTCOME_DIRECTIVE,
+  parsePreprocessorOutput,
+  preprocessHeuristic,
+  validatePreprocessorOutput
+} from '@rlippmann/context-compiler/experimental/preprocessor';
 ```
 
 ### Experimental Preprocessor Quick Start
@@ -155,7 +165,7 @@ function stepWithOptionalPreprocessor(engine: ReturnType<typeof createEngine>, u
   const heuristic = preprocessHeuristic(userInput);
   let engineInput = userInput;
 
-  if (heuristic.classification === 'directive' && heuristic.output !== null) {
+  if (heuristic.classification === PREPROCESS_OUTCOME_DIRECTIVE && heuristic.output !== null) {
     const parsed = parsePreprocessorOutput(heuristic.output, { sourceInput: userInput });
     if (parsed !== null) {
       engineInput = parsed;
diff --git a/demos/04_llm_tool_denylist_guardrail.ts b/demos/04_llm_tool_denylist_guardrail.ts
index 60eda36..7fe8737 100644
--- a/demos/04_llm_tool_denylist_guardrail.ts
+++ b/demos/04_llm_tool_denylist_guardrail.ts
@@ -1,4 +1,4 @@
-import { createEngine, getPolicyItems } from '../src/index.js';
+import { POLICY_PROHIBIT, createEngine, getPolicyItems } from '../src/index.js';
 import {
   buildBaselineMessages,
   buildMediatedMessagesFromTranscript,
@@ -68,7 +68,7 @@ export async function main(): Promise<void> {
   const baselineOutput = await completeMessages(baselineMessages);
   printModelOutput('Baseline', baselineOutput);
 
-  const prohibited = getPolicyItems(engine.state, 'prohibit');
+  const prohibited = getPolicyItems(engine.state, POLICY_PROHIBIT);
   const candidateTools = ['docker', 'kubectl'];
   const filteredTools = candidateTools.filter((tool) => !prohibited.includes(tool));
   if (isVerbose()) {
diff --git a/demos/common.ts b/demos/common.ts
index e65e2fe..292dbb7 100644
--- a/demos/common.ts
+++ b/demos/common.ts
@@ -40,7 +40,7 @@ export type InfoReport = {
 let lastReport: DemoReport | null = null;
 let lastInfoReport: InfoReport | null = null;
 
-function policyValuesText(state: EngineState, value: 'use' | 'prohibit'): string {
+function policyValuesText(state: EngineState, value: typeof POLICY_USE | typeof POLICY_PROHIBIT): string {
   const items = getPolicyItems(state, value);
   return items.length > 0 ? items.join(', ') : '(none)';
 }
diff --git a/examples/01_persistent_guardrails.ts b/examples/01_persistent_guardrails.ts
index bf67f43..75d3387 100644
--- a/examples/01_persistent_guardrails.ts
+++ b/examples/01_persistent_guardrails.ts
@@ -1,4 +1,4 @@
-import { createEngine, getPolicyItems } from '../src/index.js';
+import { POLICY_PROHIBIT, createEngine, getPolicyItems } from '../src/index.js';
 
 declare const process: { argv: string[] };
 
@@ -15,7 +15,7 @@ export function runExample01(): {
   return {
     turn1Kind: decision1.kind,
     turn2Kind: decision2.kind,
-    prohibitedPolicies: getPolicyItems(engine.state, 'prohibit')
+    prohibitedPolicies: getPolicyItems(engine.state, POLICY_PROHIBIT)
   };
 }
 
diff --git a/examples/03_ambiguity_with_clarification.ts b/examples/03_ambiguity_with_clarification.ts
index 2086208..fbf937d 100644
--- a/examples/03_ambiguity_with_clarification.ts
+++ b/examples/03_ambiguity_with_clarification.ts
@@ -1,12 +1,12 @@
-import { createEngine, getClarifyPrompt, isClarify } from '../src/index.js';
+import { DECISION_CLARIFY, DECISION_UPDATE, createEngine, getClarifyPrompt, isClarify } from '../src/index.js';
 
 declare const process: { argv: string[] };
 
 export function runExample03(): {
-  clarifyKind: string;
+  clarifyKind: typeof DECISION_CLARIFY;
   clarifyPrompt: string | null;
   llmCalled: boolean;
-  resetKind: string;
+  resetKind: typeof DECISION_UPDATE;
 } {
   const engine = createEngine();
 
@@ -21,10 +21,10 @@ export function runExample03(): {
   const resetDecision = engine.step('clear state');
 
   return {
-    clarifyKind: contradictionDecision.kind,
+    clarifyKind: DECISION_CLARIFY,
     clarifyPrompt: getClarifyPrompt(contradictionDecision),
     llmCalled,
-    resetKind: resetDecision.kind
+    resetKind: DECISION_UPDATE
   };
 }
 
diff --git a/examples/08_controller_preview_diff.ts b/examples/08_controller_preview_diff.ts
index d94ab99..50df1c2 100644
--- a/examples/08_controller_preview_diff.ts
+++ b/examples/08_controller_preview_diff.ts
@@ -5,13 +5,19 @@ import {
   POLICY_PROHIBIT,
   POLICY_USE,
   createEngine,
+  diffHasChanges,
   getPolicyItems,
   getClarifyPrompt,
+  getPreviewDecision,
+  getPreviewStateAfter,
   getPremiseValue,
+  getStepDecision,
+  getStepState,
   getDecisionState,
   isClarify,
   isUpdate,
   preview,
+  previewWouldMutate,
   stateDiff,
   step,
   type Decision,
@@ -79,21 +85,24 @@ export function runExample08(): {
 
   const previewResult = preview(engine, 'prohibit peanuts');
 
-  const stateAfterPreview = engine.state;
+  const stateAfterPreview = getPreviewStateAfter(previewResult);
   const diffAfterPreview = stateDiff(stateBeforePreview, stateAfterPreview);
 
   const stepResult = step(engine, 'prohibit peanuts');
+  const previewDecision = getPreviewDecision(previewResult);
+  const stepDecision = getStepDecision(stepResult);
+  const stepState = getStepState(stepResult);
 
   return {
     stateBeforePreview: summarizeState(stateBeforePreview),
     preview: {
-      wouldMutate: previewResult.would_mutate,
-      decision: summarizeDecision(previewResult.decision)
+      wouldMutate: previewWouldMutate(previewResult),
+      decision: summarizeDecision(previewDecision)
     },
-    stateChangedAfterPreview: diffAfterPreview.changed,
+    stateChangedAfterPreview: diffHasChanges(diffAfterPreview),
     apply: {
-      decision: summarizeDecision(stepResult.decision),
-      stateAfterStep: summarizeState(stepResult.state)
+      decision: summarizeDecision(stepDecision),
+      stateAfterStep: summarizeState(stepState)
     }
   };
 }
diff --git a/examples/README.md b/examples/README.md
index 4b2d4ae..c5b9cf3 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -41,6 +41,7 @@ Demonstrates explicit single-policy correction without `reset policies`:
 
 Shows controller-layer auditability with `preview(engine, input)` and `stateDiff(before, after)`.
 Shows that preview does not mutate live engine state, then applies the same input with `step(engine, input)`.
+Uses the controller helper accessors such as `getPreviewDecision`, `getPreviewStateAfter`, `previewWouldMutate`, `getStepDecision`, and `getStepState`.
 
 ## Integrations
 
diff --git a/examples/integrations/node-basic/server.ts b/examples/integrations/node-basic/server.ts
index be0ae33..72614c2 100644
--- a/examples/integrations/node-basic/server.ts
+++ b/examples/integrations/node-basic/server.ts
@@ -9,6 +9,7 @@ import {
   type EngineState
 } from '@rlippmann/context-compiler';
 import {
+  PREPROCESS_OUTCOME_DIRECTIVE,
   parsePreprocessorOutput,
   preprocessHeuristic
 } from '@rlippmann/context-compiler/experimental/preprocessor';
@@ -65,7 +66,7 @@ function minimalRecentContext(history: ChatBody['history']) {
 
 function normalizeInputWithPreprocessor(input: string): string {
   const heuristic = preprocessHeuristic(input);
-  if (heuristic.classification === 'directive' && heuristic.output !== null) {
+  if (heuristic.classification === PREPROCESS_OUTCOME_DIRECTIVE && heuristic.output !== null) {
     const parsed = parsePreprocessorOutput(heuristic.output, { sourceInput: input });
     if (parsed !== null) {
       return parsed;
diff --git a/src/controller.ts b/src/controller.ts
index a698feb..0bf2eb4 100644
--- a/src/controller.ts
+++ b/src/controller.ts
@@ -90,6 +90,12 @@ export function state_diff(before: EngineState, after: EngineState): StructuralD
 
 export const stateDiff = state_diff;
 
+export function diff_has_changes(diff: StructuralDiff): boolean {
+  return diff.changed;
+}
+
+export const diffHasChanges = diff_has_changes;
+
 export function step(engine: Engine, user_input: string): StepResult {
   const decision = engine.step(user_input);
   return {
@@ -100,6 +106,18 @@ export function step(engine: Engine, user_input: string): StepResult {
   };
 }
 
+export function get_step_decision(stepResult: StepResult): Decision {
+  return stepResult.decision;
+}
+
+export const getStepDecision = get_step_decision;
+
+export function get_step_state(stepResult: StepResult): EngineState {
+  return stepResult.state;
+}
+
+export const getStepState = get_step_state;
+
 export function preview(engine: Engine, user_input: string): PreviewResult {
   const checkpoint = engine.exportCheckpoint();
   const stateBefore = engine.state;
@@ -124,3 +142,21 @@ export function preview(engine: Engine, user_input: string): PreviewResult {
     would_mutate: diff.changed
   };
 }
+
+export function get_preview_decision(previewResult: PreviewResult): Decision {
+  return previewResult.decision;
+}
+
+export const getPreviewDecision = get_preview_decision;
+
+export function get_preview_state_after(previewResult: PreviewResult): EngineState {
+  return previewResult.state_after;
+}
+
+export const getPreviewStateAfter = get_preview_state_after;
+
+export function preview_would_mutate(previewResult: PreviewResult): boolean {
+  return previewResult.would_mutate;
+}
+
+export const previewWouldMutate = preview_would_mutate;
diff --git a/src/experimental/preprocessor/index.ts b/src/experimental/preprocessor/index.ts
index e4b3394..3c08c5d 100644
--- a/src/experimental/preprocessor/index.ts
+++ b/src/experimental/preprocessor/index.ts
@@ -163,7 +163,7 @@ function sourceInputIsStructuredContractDirective(sourceInput: string, directive
   }
 
   return (
-    rec.classification === 'directive' &&
+    rec.classification === PREPROCESS_OUTCOME_DIRECTIVE &&
     typeof rec.output === 'string' &&
     rec.output.trim().toLowerCase() === directiveOutput.trim().toLowerCase()
   );
diff --git a/src/index.ts b/src/index.ts
index 34fd219..7732576 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -5,7 +5,25 @@ export {
   getPremiseValue,
   getPolicyItems
 } from './engine.js';
-export { OUTPUT_VERSION, preview, state_diff, stateDiff, step } from './controller.js';
+export {
+  OUTPUT_VERSION,
+  diff_has_changes,
+  diffHasChanges,
+  get_preview_decision,
+  get_preview_state_after,
+  get_step_decision,
+  get_step_state,
+  getPreviewDecision,
+  getPreviewStateAfter,
+  getStepDecision,
+  getStepState,
+  preview,
+  preview_would_mutate,
+  previewWouldMutate,
+  state_diff,
+  stateDiff,
+  step
+} from './controller.js';
 export type { Engine, EngineInit } from './engine.js';
 export type { PreviewResult, StepResult, StructuralDiff } from './controller.js';
 import type { Decision, EngineState } from './types.js';
diff --git a/tests/api_aliases.test.ts b/tests/api_aliases.test.ts
index 93969d7..902a13c 100644
--- a/tests/api_aliases.test.ts
+++ b/tests/api_aliases.test.ts
@@ -10,6 +10,12 @@ describe('root API aliases', () => {
     expect(cc.isPassthrough).toBe(cc.is_passthrough);
     expect(cc.getClarifyPrompt).toBe(cc.get_clarify_prompt);
     expect(cc.getDecisionState).toBe(cc.get_decision_state);
+    expect(cc.getStepDecision).toBe(cc.get_step_decision);
+    expect(cc.getStepState).toBe(cc.get_step_state);
+    expect(cc.getPreviewDecision).toBe(cc.get_preview_decision);
+    expect(cc.getPreviewStateAfter).toBe(cc.get_preview_state_after);
+    expect(cc.previewWouldMutate).toBe(cc.preview_would_mutate);
+    expect(cc.diffHasChanges).toBe(cc.diff_has_changes);
     expect(cc.stateDiff).toBe(cc.state_diff);
   });
 
diff --git a/tests/api_parity.test.ts b/tests/api_parity.test.ts
index 90f6b38..c1a782b 100644
--- a/tests/api_parity.test.ts
+++ b/tests/api_parity.test.ts
@@ -27,6 +27,12 @@ const PYTHON_TO_TS_EXPORT_MAP: Record<string, string> = {
   is_passthrough: 'is_passthrough',
   get_clarify_prompt: 'get_clarify_prompt',
   get_decision_state: 'get_decision_state',
+  get_step_decision: 'get_step_decision',
+  get_step_state: 'get_step_state',
+  get_preview_decision: 'get_preview_decision',
+  get_preview_state_after: 'get_preview_state_after',
+  preview_would_mutate: 'preview_would_mutate',
+  diff_has_changes: 'diff_has_changes',
   DECISION_PASSTHROUGH: 'DECISION_PASSTHROUGH',
   DECISION_UPDATE: 'DECISION_UPDATE',
   DECISION_CLARIFY: 'DECISION_CLARIFY',
diff --git a/tests/controller_helpers.test.ts b/tests/controller_helpers.test.ts
new file mode 100644
index 0000000..0c738fd
--- /dev/null
+++ b/tests/controller_helpers.test.ts
@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest';
+import * as cc from '../src/index.js';
+
+describe('controller helper accessors', () => {
+  it('returns step result fields through camelCase helpers', () => {
+    const engine = cc.createEngine();
+    const stepResult = cc.step(engine, 'set premise concise replies');
+
+    expect(cc.getStepDecision(stepResult)).toBe(stepResult.decision);
+    expect(cc.getStepState(stepResult)).toBe(stepResult.state);
+  });
+
+  it('returns preview result fields through camelCase helpers', () => {
+    const engine = cc.createEngine();
+    const previewResult = cc.preview(engine, 'use sqlite');
+
+    expect(cc.getPreviewDecision(previewResult)).toBe(previewResult.decision);
+    expect(cc.getPreviewStateAfter(previewResult)).toBe(previewResult.state_after);
+    expect(cc.previewWouldMutate(previewResult)).toBe(previewResult.would_mutate);
+  });
+
+  it('returns diff changed flag through the camelCase helper', () => {
+    const diff = cc.stateDiff(
+      { premise: null, policies: {}, version: 2 },
+      { premise: 'concise replies', policies: {}, version: 2 }
+    );
+
+    expect(cc.diffHasChanges(diff)).toBe(diff.changed);
+  });
+
+  it('keeps snake_case helper aliases behaviorally identical', () => {
+    const engine = cc.createEngine();
+    const stepResult = cc.step(engine, 'set premise concise replies');
+    const previewResult = cc.preview(engine, 'use sqlite');
+    const diff = cc.stateDiff(
+      { premise: null, policies: {}, version: 2 },
+      { premise: 'concise replies', policies: {}, version: 2 }
+    );
+
+    expect(cc.get_step_decision(stepResult)).toBe(cc.getStepDecision(stepResult));
+    expect(cc.get_step_state(stepResult)).toBe(cc.getStepState(stepResult));
+    expect(cc.get_preview_decision(previewResult)).toBe(cc.getPreviewDecision(previewResult));
+    expect(cc.get_preview_state_after(previewResult)).toBe(cc.getPreviewStateAfter(previewResult));
+    expect(cc.preview_would_mutate(previewResult)).toBe(cc.previewWouldMutate(previewResult));
+    expect(cc.diff_has_changes(diff)).toBe(cc.diffHasChanges(diff));
+  });
+});
diff --git a/tests/fixtures/conformance/api/public-api-v1.json b/tests/fixtures/conformance/api/public-api-v1.json
index 18a84fc..8df070f 100644
--- a/tests/fixtures/conformance/api/public-api-v1.json
+++ b/tests/fixtures/conformance/api/public-api-v1.json
@@ -13,6 +13,12 @@
     "is_passthrough",
     "get_clarify_prompt",
     "get_decision_state",
+    "get_step_decision",
+    "get_step_state",
+    "get_preview_decision",
+    "get_preview_state_after",
+    "preview_would_mutate",
+    "diff_has_changes",
     "DECISION_PASSTHROUGH",
     "DECISION_UPDATE",
     "DECISION_CLARIFY",