feat(omo-codex): add post-compact rule budget to codex hook

Trim rule and result char budgets after compaction via new
postCompactMaxRuleChars/postCompactMaxResultChars config, applied
through withPostCompactBudget. Extract codex-hook helpers into
dynamic-target-fingerprints, hook-output, path-utils,
rules-engine-factory, and transcript-rule-filter modules.

packages/omo-codex/plugin/components/rules/src/codex-hook.ts

@@ -1,8 +1,8 @@
-import { readFileSync, statSync } from "node:fs";
-import { isAbsolute, relative, resolve } from "node:path";
-
 import { configFromEnvironment } from "./config.js";
 import { createHookDebugTimer } from "./debug-log.js";
+import { fingerprintDynamicTargets } from "./dynamic-target-fingerprints.js";
+import { formatAdditionalContextOutput } from "./hook-output.js";
+import { displayPath, uniqueStrings } from "./path-utils.js";
 import {
 	clearSessionState,
 	hasPostCompactPending,
@@ -12,18 +12,11 @@ import {
 	persistEngineState,
 	sessionCachePath,
 } from "./persistent-cache.js";
-import { SOURCE_PRIORITY } from "./rules/constants.js";
+import { withPostCompactBudget } from "./post-compact-budget.js";
-import { createEngine } from "./rules/engine.js";
+import { createRulesEngine } from "./rules-engine-factory.js";
-import { createRuleDiscoveryCache, findRuleCandidates } from "./rules/finder.js";
-import { hashContent } from "./rules/matcher.js";
-import { sortCandidates } from "./rules/ordering.js";
-import { findProjectRoot } from "./rules/project-root.js";
-import type { LoadedRule, PiRulesConfig, RuleCandidate } from "./rules/types.js";
 import { extractCodexToolPaths } from "./tool-paths.js";
+import { filterRulesAlreadyInTranscript } from "./transcript-rule-filter.js";
 import type { TranscriptSearchOptions } from "./transcript-search.js";
-import { readTranscriptSearchText } from "./transcript-search.js";
-
-type ContextInjectionHookEventName = "SessionStart" | "UserPromptSubmit" | "PostToolUse";
 
 export type CodexSessionStartInput = {
 	session_id: string;
@@ -75,12 +68,6 @@ export interface CodexRulesHookOptions {
 	pluginDataRoot?: string;
 }
 
-interface DynamicTargetFingerprint {
-	targetPath: string;
-	cacheKey: string;
-	fingerprint: string;
-}
-
 export async function runSessionStartHook(
 	input: CodexSessionStartInput,
 	options: CodexRulesHookOptions = {},
@@ -155,7 +142,7 @@ export async function runPostToolUseHook(
 
 	const cachePath = sessionCachePath(input.session_id, options.pluginDataRoot);
 	const postCompactPending = isPostCompactPending(cachePath, "dynamic");
-	const engine = createRulesEngine(options);
+	const engine = createRulesEngine(options, postCompactPending ? withPostCompactBudget(config) : config);
 	hydrateEngineState(engine, cachePath);
 	debugTimer.lap("hydrate", {
 		dynamicDedupScopes: engine.state.dynamicDedup.size,
@@ -226,7 +213,8 @@ function runStaticInjection(
 		return "";
 	}
 
-	const engine = createRulesEngine(options);
+	const effectiveConfig = completedPostCompactChannel === undefined ? config : withPostCompactBudget(config);
+	const engine = createRulesEngine(options, effectiveConfig);
 	hydrateEngineState(engine, cachePath);
 	engine.state.cwd = cwd;
 
@@ -251,183 +239,3 @@ function runStaticInjection(
 	persistEngineState(engine, cachePath, completedPostCompactChannel);
 	return formatAdditionalContextOutput(eventName, block);
 }
-
-function filterRulesAlreadyInTranscript(
-	rules: ReadonlyArray<LoadedRule>,
-	transcriptPath: string | null,
-	markInjected: (rule: LoadedRule) => void,
-	options: TranscriptSearchOptions = {},
-): LoadedRule[] {
-	if (rules.length === 0 || transcriptPath === null) {
-		return [...rules];
-	}
-
-	const transcriptText = readTranscriptSearchText(transcriptPath, options);
-	if (transcriptText === null) {
-		return [...rules];
-	}
-
-	const pendingRules: LoadedRule[] = [];
-	for (const rule of rules) {
-		if (isRuleAlreadyInTranscript(rule, transcriptText)) {
-			markInjected(rule);
-			continue;
-		}
-
-		pendingRules.push(rule);
-	}
-	return pendingRules;
-}
-
-function isRuleAlreadyInTranscript(rule: LoadedRule, transcriptText: string): boolean {
-	const bodyNeedle = rule.body.trim().slice(0, 2_000);
-	if (bodyNeedle.length === 0 || !transcriptText.includes(bodyNeedle)) {
-		return false;
-	}
-
-	const markers = [
-		`Instructions from: ${rule.path}`,
-		`Instructions from: ${rule.realPath}`,
-		rule.relativePath.length === 0 ? null : rule.relativePath,
-	].filter((marker): marker is string => marker !== null);
-	return markers.some((marker) => transcriptText.includes(marker));
-}
-
-function createRulesEngine(options: CodexRulesHookOptions) {
-	const config = configFromEnvironment(options.env);
-	return createEngine(config, {
-		findCandidates: findRuleCandidates,
-		findProjectRoot,
-		readFile: (path) => {
-			try {
-				return readFileSync(path, "utf8");
-			} catch {
-				return null;
-			}
-		},
-	});
-}
-
-function fingerprintDynamicTargets(
-	cwd: string,
-	targetPaths: ReadonlyArray<string>,
-	config: PiRulesConfig,
-): DynamicTargetFingerprint[] {
-	const disabledSources = disabledSourcesFor(config);
-	const discoveryCache = createRuleDiscoveryCache();
-	const cwdProjectRoot = findProjectRoot(cwd);
-	const fingerprints: DynamicTargetFingerprint[] = [];
-
-	for (const targetPath of uniqueStrings(targetPaths)) {
-		const projectRoot =
-			cwdProjectRoot !== null && isSameOrChildPath(targetPath, cwdProjectRoot)
-				? cwdProjectRoot
-				: findProjectRoot(targetPath);
-		const findOptions: {
-			projectRoot: string | null;
-			targetFile: string;
-			disabledSources?: ReadonlySet<string>;
-			cache: ReturnType<typeof createRuleDiscoveryCache>;
-		} = {
-			projectRoot,
-			targetFile: targetPath,
-			cache: discoveryCache,
-		};
-		if (disabledSources !== undefined) {
-			findOptions.disabledSources = disabledSources;
-		}
-		const candidates = findRuleCandidates(findOptions);
-		const candidateFingerprint = sortCandidates(candidates).map(fingerprintCandidate).join("\u0001");
-		const cacheKey = dynamicTargetCacheKey(targetPath);
-		fingerprints.push({
-			targetPath,
-			cacheKey,
-			fingerprint: hashContent(
-				[
-					"v1",
-					config.enabledSources === "auto" ? "auto" : config.enabledSources.join(","),
-					projectRoot ?? "",
-					cacheKey,
-					candidateFingerprint,
-				].join("\u0000"),
-			),
-		});
-	}
-
-	return fingerprints;
-}
-
-function fingerprintCandidate(candidate: RuleCandidate): string {
-	return [
-		candidate.realPath,
-		candidate.relativePath,
-		candidate.source,
-		candidate.isGlobal ? "global" : "project",
-		candidate.isSingleFile ? "single" : "multi",
-		String(candidate.distance),
-		fileFingerprint(candidate.path),
-	].join("\u0000");
-}
-
-function fileFingerprint(filePath: string): string {
-	try {
-		const stats = statSync(filePath, { bigint: true });
-		return `${stats.mtimeNs}:${stats.ctimeNs}:${stats.size}`;
-	} catch {
-		return "missing";
-	}
-}
-
-function disabledSourcesFor(config: PiRulesConfig): ReadonlySet<string> | undefined {
-	if (config.enabledSources === "auto") {
-		return undefined;
-	}
-
-	const enabledSources = new Set(config.enabledSources);
-	return new Set([...SOURCE_PRIORITY.keys()].filter((source) => !enabledSources.has(source)));
-}
-
-function dynamicTargetCacheKey(targetPath: string): string {
-	return toPosixPath(resolve(targetPath));
-}
-
-function isSameOrChildPath(childPath: string, parentPath: string): boolean {
-	const childRelativePath = relative(parentPath, resolve(childPath));
-	return childRelativePath === "" || (!childRelativePath.startsWith("..") && !isAbsolute(childRelativePath));
-}
-
-function uniqueStrings(values: ReadonlyArray<string>): string[] {
-	const uniqueValues: string[] = [];
-	const seenValues = new Set<string>();
-	for (const value of values) {
-		if (seenValues.has(value)) {
-			continue;
-		}
-
-		seenValues.add(value);
-		uniqueValues.push(value);
-	}
-	return uniqueValues;
-}
-
-function formatAdditionalContextOutput(eventName: ContextInjectionHookEventName, additionalContext: string): string {
-	if (additionalContext.trim().length === 0) return "";
-	return `${JSON.stringify({
-		hookSpecificOutput: {
-			hookEventName: eventName,
-			additionalContext,
-		},
-	})}\n`;
-}
-
-function displayPath(cwd: string, filePath: string): string {
-	const rel = isAbsolute(filePath) ? relative(cwd, filePath) : filePath;
-	// Normalize to POSIX separators so injected rule context renders the same
-	// path string on Linux/macOS and Windows (Codex feeds this verbatim into
-	// the model prompt, and the existing engine already emits POSIX paths).
-	return toPosixPath(rel);
-}
-
-function toPosixPath(path: string): string {
-	return path.replaceAll("\\", "/");
-}

packages/omo-codex/plugin/components/rules/src/config.ts

@@ -13,6 +13,14 @@ export function configFromEnvironment(env: NodeJS.ProcessEnv = process.env): PiR
 	config.maxResultChars =
 		parsePositiveInteger(firstEnv(env, "CODEX_RULES_MAX_RESULT_CHARS", "PI_RULES_MAX_RESULT_CHARS")) ??
 		config.maxResultChars;
+	config.postCompactMaxRuleChars =
+		parsePositiveInteger(
+			firstEnv(env, "CODEX_RULES_POST_COMPACT_MAX_RULE_CHARS", "PI_RULES_POST_COMPACT_MAX_RULE_CHARS"),
+		) ?? config.postCompactMaxRuleChars;
+	config.postCompactMaxResultChars =
+		parsePositiveInteger(
+			firstEnv(env, "CODEX_RULES_POST_COMPACT_MAX_RESULT_CHARS", "PI_RULES_POST_COMPACT_MAX_RESULT_CHARS"),
+		) ?? config.postCompactMaxResultChars;
 	config.enabledSources = parseEnabledSources(
 		firstEnv(env, "CODEX_RULES_ENABLED_SOURCES", "PI_RULES_ENABLED_SOURCES"),
 		disableBundledRules,

packages/omo-codex/plugin/components/rules/src/dynamic-target-fingerprints.ts

@@ -0,0 +1,98 @@
+import { statSync } from "node:fs";
+import { resolve } from "node:path";
+import { isSameOrChildPath, toPosixPath, uniqueStrings } from "./path-utils.js";
+import { SOURCE_PRIORITY } from "./rules/constants.js";
+import { createRuleDiscoveryCache, findRuleCandidates } from "./rules/finder.js";
+import { hashContent } from "./rules/matcher.js";
+import { sortCandidates } from "./rules/ordering.js";
+import { findProjectRoot } from "./rules/project-root.js";
+import type { PiRulesConfig, RuleCandidate } from "./rules/types.js";
+
+export interface DynamicTargetFingerprint {
+	targetPath: string;
+	cacheKey: string;
+	fingerprint: string;
+}
+
+export function fingerprintDynamicTargets(
+	cwd: string,
+	targetPaths: ReadonlyArray<string>,
+	config: PiRulesConfig,
+): DynamicTargetFingerprint[] {
+	const disabledSources = disabledSourcesFor(config);
+	const discoveryCache = createRuleDiscoveryCache();
+	const cwdProjectRoot = findProjectRoot(cwd);
+	const fingerprints: DynamicTargetFingerprint[] = [];
+
+	for (const targetPath of uniqueStrings(targetPaths)) {
+		const projectRoot =
+			cwdProjectRoot !== null && isSameOrChildPath(targetPath, cwdProjectRoot)
+				? cwdProjectRoot
+				: findProjectRoot(targetPath);
+		const findOptions: {
+			projectRoot: string | null;
+			targetFile: string;
+			disabledSources?: ReadonlySet<string>;
+			cache: ReturnType<typeof createRuleDiscoveryCache>;
+		} = {
+			projectRoot,
+			targetFile: targetPath,
+			cache: discoveryCache,
+		};
+		if (disabledSources !== undefined) {
+			findOptions.disabledSources = disabledSources;
+		}
+		const candidates = findRuleCandidates(findOptions);
+		const candidateFingerprint = sortCandidates(candidates).map(fingerprintCandidate).join("\u0001");
+		const cacheKey = dynamicTargetCacheKey(targetPath);
+		fingerprints.push({
+			targetPath,
+			cacheKey,
+			fingerprint: hashContent(
+				[
+					"v1",
+					config.enabledSources === "auto" ? "auto" : config.enabledSources.join(","),
+					projectRoot ?? "",
+					cacheKey,
+					candidateFingerprint,
+				].join("\u0000"),
+			),
+		});
+	}
+
+	return fingerprints;
+}
+
+function fingerprintCandidate(candidate: RuleCandidate): string {
+	return [
+		candidate.realPath,
+		candidate.relativePath,
+		candidate.source,
+		candidate.isGlobal ? "global" : "project",
+		candidate.isSingleFile ? "single" : "multi",
+		String(candidate.distance),
+		fileFingerprint(candidate.path),
+	].join("\u0000");
+}
+
+function fileFingerprint(filePath: string): string {
+	try {
+		const stats = statSync(filePath, { bigint: true });
+		return `${stats.mtimeNs}:${stats.ctimeNs}:${stats.size}`;
+	} catch {
+		return "missing";
+	}
+}
+
+function disabledSourcesFor(config: PiRulesConfig): ReadonlySet<string> | undefined {
+	if (config.enabledSources === "auto") {
+		return undefined;
+	}
+
+	const enabledSources = new Set(config.enabledSources);
+	return new Set([...SOURCE_PRIORITY.keys()].filter((source) => !enabledSources.has(source)));
+}
+
+function dynamicTargetCacheKey(targetPath: string): string {
+	return toPosixPath(resolve(targetPath));
+}

packages/omo-codex/plugin/components/rules/src/hook-output.ts

@@ -0,0 +1,14 @@
+export type ContextInjectionHookEventName = "SessionStart" | "UserPromptSubmit" | "PostToolUse";
+
+export function formatAdditionalContextOutput(
+	eventName: ContextInjectionHookEventName,
+	additionalContext: string,
+): string {
+	if (additionalContext.trim().length === 0) return "";
+	return `${JSON.stringify({
+		hookSpecificOutput: {
+			hookEventName: eventName,
+			additionalContext,
+		},
+	})}\n`;
+}

packages/omo-codex/plugin/components/rules/src/path-utils.ts

@@ -0,0 +1,29 @@
+import { isAbsolute, relative, resolve } from "node:path";
+
+export function displayPath(cwd: string, filePath: string): string {
+	const rel = isAbsolute(filePath) ? relative(cwd, filePath) : filePath;
+	return toPosixPath(rel);
+}
+
+export function isSameOrChildPath(childPath: string, parentPath: string): boolean {
+	const childRelativePath = relative(parentPath, resolve(childPath));
+	return childRelativePath === "" || (!childRelativePath.startsWith("..") && !isAbsolute(childRelativePath));
+}
+
+export function toPosixPath(path: string): string {
+	return path.replaceAll("\\", "/");
+}
+
+export function uniqueStrings(values: ReadonlyArray<string>): string[] {
+	const uniqueValues: string[] = [];
+	const seenValues = new Set<string>();
+	for (const value of values) {
+		if (seenValues.has(value)) {
+			continue;
+		}
+
+		seenValues.add(value);
+		uniqueValues.push(value);
+	}
+	return uniqueValues;
+}

packages/omo-codex/plugin/components/rules/src/post-compact-budget.ts

@@ -0,0 +1,9 @@
+import type { PiRulesConfig } from "./rules/types.js";
+
+export function withPostCompactBudget(config: PiRulesConfig): PiRulesConfig {
+	return {
+		...config,
+		maxRuleChars: Math.min(config.maxRuleChars, config.postCompactMaxRuleChars),
+		maxResultChars: Math.min(config.maxResultChars, config.postCompactMaxResultChars),
+	};
+}

packages/omo-codex/plugin/components/rules/src/rules-engine-factory.ts

@@ -0,0 +1,24 @@
+import { readFileSync } from "node:fs";
+
+import { configFromEnvironment } from "./config.js";
+import { createEngine } from "./rules/engine.js";
+import { findRuleCandidates } from "./rules/finder.js";
+import { findProjectRoot } from "./rules/project-root.js";
+
+interface RulesEngineFactoryOptions {
+	env?: NodeJS.ProcessEnv;
+}
+
+export function createRulesEngine(options: RulesEngineFactoryOptions, config = configFromEnvironment(options.env)) {
+	return createEngine(config, {
+		findCandidates: findRuleCandidates,
+		findProjectRoot,
+		readFile: (path) => {
+			try {
+				return readFileSync(path, "utf8");
+			} catch {
+				return null;
+			}
+		},
+	});
+}

packages/omo-codex/plugin/components/rules/src/rules/constants.ts

@@ -92,6 +92,10 @@ export const DEFAULT_MAX_SCAN_FILES = 1000;
  */
 export const DEFAULT_MAX_RESULT_CHARS = 40000;
 
+export const DEFAULT_POST_COMPACT_MAX_RULE_CHARS = 6000;
+
+export const DEFAULT_POST_COMPACT_MAX_RESULT_CHARS = 12000;
+
 /**
  * Truncation marker template. `{path}` is replaced with the relative path.
  */

packages/omo-codex/plugin/components/rules/src/rules/engine.ts

@@ -12,6 +12,8 @@ import {
 import {
 	DEFAULT_MAX_RESULT_CHARS,
 	DEFAULT_MAX_RULE_CHARS,
+	DEFAULT_POST_COMPACT_MAX_RESULT_CHARS,
+	DEFAULT_POST_COMPACT_MAX_RULE_CHARS,
 	PROJECT_SINGLE_FILES,
 	SOURCE_PRIORITY,
 } from "./constants.js";
@@ -74,6 +76,8 @@ export function defaultConfig(): PiRulesConfig {
 		mode: "both",
 		maxRuleChars: DEFAULT_MAX_RULE_CHARS,
 		maxResultChars: DEFAULT_MAX_RESULT_CHARS,
+		postCompactMaxRuleChars: DEFAULT_POST_COMPACT_MAX_RULE_CHARS,
+		postCompactMaxResultChars: DEFAULT_POST_COMPACT_MAX_RESULT_CHARS,
 		enabledSources: "auto",
 	};
 }

packages/omo-codex/plugin/components/rules/src/rules/types.ts

@@ -114,6 +114,8 @@ export interface PiRulesConfig {
 	mode: "static" | "dynamic" | "both" | "off";
 	maxRuleChars: number;
 	maxResultChars: number;
+	postCompactMaxRuleChars: number;
+	postCompactMaxResultChars: number;
 	enabledSources: RuleSource[] | "auto";
 }
 

packages/omo-codex/plugin/components/rules/src/transcript-rule-filter.ts

@@ -0,0 +1,44 @@
+import type { LoadedRule } from "./rules/types.js";
+import type { TranscriptSearchOptions } from "./transcript-search.js";
+import { readTranscriptSearchText } from "./transcript-search.js";
+
+export function filterRulesAlreadyInTranscript(
+	rules: ReadonlyArray<LoadedRule>,
+	transcriptPath: string | null,
+	markInjected: (rule: LoadedRule) => void,
+	options: TranscriptSearchOptions = {},
+): LoadedRule[] {
+	if (rules.length === 0 || transcriptPath === null) {
+		return [...rules];
+	}
+
+	const transcriptText = readTranscriptSearchText(transcriptPath, options);
+	if (transcriptText === null) {
+		return [...rules];
+	}
+
+	const pendingRules: LoadedRule[] = [];
+	for (const rule of rules) {
+		if (isRuleAlreadyInTranscript(rule, transcriptText)) {
+			markInjected(rule);
+			continue;
+		}
+
+		pendingRules.push(rule);
+	}
+	return pendingRules;
+}
+
+function isRuleAlreadyInTranscript(rule: LoadedRule, transcriptText: string): boolean {
+	const bodyNeedle = rule.body.trim().slice(0, 2_000);
+	if (bodyNeedle.length === 0 || !transcriptText.includes(bodyNeedle)) {
+		return false;
+	}
+
+	const markers = [
+		`Instructions from: ${rule.path}`,
+		`Instructions from: ${rule.realPath}`,
+		rule.relativePath.length === 0 ? null : rule.relativePath,
+	].filter((marker): marker is string => marker !== null);
+	return markers.some((marker) => transcriptText.includes(marker));
+}

packages/omo-codex/plugin/components/rules/test/codex-hook-post-compact-budget.test.ts

@@ -0,0 +1,136 @@
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import path from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+
+import {
+	type CodexPostCompactInput,
+	type CodexSessionStartInput,
+	runPostCompactHook,
+	runSessionStartHook,
+	runUserPromptSubmitHook,
+} from "../src/codex-hook.js";
+
+const tempDirectories: string[] = [];
+const PROJECT_RULES_ENV = {
+	CODEX_RULES_ENABLED_SOURCES: "AGENTS.md,.omo/rules",
+	CODEX_RULES_MAX_RESULT_CHARS: "50000",
+	CODEX_RULES_MAX_RULE_CHARS: "30000",
+};
+
+afterEach(() => {
+	for (const directory of tempDirectories.splice(0)) {
+		rmSync(directory, { recursive: true, force: true });
+	}
+});
+
+describe("codex rules post-compaction context budget", () => {
+	it("#given oversized project rules after compaction #when static rules re-inject #then output uses the post-compact budget", async () => {
+		// given
+		const { root, pluginData } = makeOversizedProject();
+		const firstOutput = await runSessionStartHook(sessionStartInput(root), {
+			pluginDataRoot: pluginData,
+			env: PROJECT_RULES_ENV,
+		});
+		const firstContext = readAdditionalContext(firstOutput);
+		const transcriptPath = writeCompactedTranscript(root, "summary dropped injected rules");
+		await runPostCompactHook(
+			{ ...postCompactInput(root), transcript_path: transcriptPath },
+			{ pluginDataRoot: pluginData },
+		);
+
+		// when
+		const output = await runUserPromptSubmitHook(userPromptSubmitInput(root, transcriptPath), {
+			pluginDataRoot: pluginData,
+			env: PROJECT_RULES_ENV,
+		});
+
+		// then
+		const postCompactContext = readAdditionalContext(output);
+		expect(firstContext.length).toBeGreaterThan(20_000);
+		expect(postCompactContext.length).toBeLessThan(firstContext.length);
+		expect(postCompactContext.length).toBeLessThan(14_000);
+		expect(postCompactContext).toContain("[Rule truncated. Read full rule:");
+		expect(postCompactContext).toContain("Instructions from:");
+	});
+});
+
+function makeOversizedProject(): { root: string; pluginData: string } {
+	const root = mkdtempSync(path.join(tmpdir(), "codex-rules-post-compact-budget-project-"));
+	const pluginData = mkdtempSync(path.join(tmpdir(), "codex-rules-post-compact-budget-data-"));
+	tempDirectories.push(root, pluginData);
+	writeFileSync(path.join(root, "package.json"), JSON.stringify({ name: "fixture" }));
+	writeFileSync(path.join(root, "AGENTS.md"), `Project rule\n${"A".repeat(30_000)}`);
+	mkdirSync(path.join(root, ".omo", "rules"), { recursive: true });
+	writeFileSync(
+		path.join(root, ".omo", "rules", "typescript.md"),
+		["---", 'globs: "**/*.ts"', "---", "", `TypeScript rule\n${"B".repeat(30_000)}`].join("\n"),
+	);
+	return { root, pluginData };
+}
+
+function sessionStartInput(root: string): CodexSessionStartInput {
+	return {
+		session_id: "session-post-compact-budget",
+		transcript_path: null,
+		cwd: root,
+		hook_event_name: "SessionStart",
+		model: "gpt-5.5",
+		permission_mode: "default",
+		source: "startup",
+	};
+}
+
+function postCompactInput(root: string): CodexPostCompactInput {
+	return {
+		session_id: "session-post-compact-budget",
+		turn_id: "turn-compact",
+		transcript_path: null,
+		cwd: root,
+		hook_event_name: "PostCompact",
+		model: "gpt-5.5",
+		trigger: "auto",
+	};
+}
+
+function userPromptSubmitInput(root: string, transcriptPath: string): Parameters<typeof runUserPromptSubmitHook>[0] {
+	return {
+		session_id: "session-post-compact-budget",
+		turn_id: "turn-after-compact",
+		transcript_path: transcriptPath,
+		cwd: root,
+		hook_event_name: "UserPromptSubmit",
+		model: "gpt-5.5",
+		permission_mode: "default",
+		prompt: "continue",
+	};
+}
+
+function writeCompactedTranscript(root: string, retainedText: string): string {
+	const transcriptPath = path.join(root, "transcript-compacted.jsonl");
+	writeFileSync(
+		transcriptPath,
+		`${JSON.stringify({
+			type: "compacted",
+			payload: {
+				message: "summary",
+				replacement_history: [{ type: "message", role: "user", content: retainedText }],
+			},
+		})}\n`,
+	);
+	return transcriptPath;
+}
+
+function readAdditionalContext(output: string): string {
+	expect(output.trim().length).toBeGreaterThan(0);
+	const parsed: unknown = JSON.parse(output);
+	if (!isRecord(parsed)) return "";
+	const hookSpecificOutput = parsed["hookSpecificOutput"];
+	if (!isRecord(hookSpecificOutput)) return "";
+	const additionalContext = hookSpecificOutput["additionalContext"];
+	return typeof additionalContext === "string" ? additionalContext : "";
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+	return typeof value === "object" && value !== null && !Array.isArray(value);
+}