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feat(FN-1877): add auto-compaction on context window errors to promptWithFallback

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- Detect context-window-limit errors from AI sessions and automatically compact
  the session conversation history before retrying (one attempt per session)
- Centralize auto-compaction in promptWithFallback (pi.ts) so executor, merger,
  and step-session-executor all benefit from the same mechanism
- Remove scattered context-limit error handling from executor.ts, merger.ts, and
  step-session-executor.ts in favor of the centralized approach
- Add comprehensive tests for auto-compaction retry behavior in pi.test.ts
- Remove unused compactSessionContext import from step-session-executor.ts
- Add memory note documenting the centralized auto-compaction design
This commit is contained in:
Fusion
2026-04-15 10:42:20 -07:00
committed by gsxdsm
parent bd7ada7533
commit ddf0fc7303
7 changed files with 335 additions and 244 deletions
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106
packages/engine/src/pi.ts
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@@ -33,6 +33,7 @@ import {
createSkillsOverrideFromSelection,
type SkillSelectionContext,
} from "./skill-resolver.js";
import { isContextLimitError } from "./context-limit-detector.js";
export interface AgentResult {
session: AgentSession;
@@ -54,12 +55,42 @@ export async function promptWithFallback(session: AgentSession, prompt: string,
}
console.error(`[pi] promptWithFallback: calling session.prompt (prompt length=${prompt.length})`);
if (options === undefined) {
await session.prompt(prompt);
} else {
await (session.prompt as any)(prompt, options);
try {
if (options === undefined) {
await session.prompt(prompt);
} else {
await (session.prompt as any)(prompt, options);
}
console.error(`[pi] promptWithFallback: prompt completed`);
} catch (err: unknown) {
const errorMessage = err instanceof Error ? err.message : String(err);
if (!isContextLimitError(errorMessage)) {
console.error(`[pi] promptWithFallback: non-context error — propagating: ${errorMessage}`);
throw err;
}
// Context limit error — attempt auto-compaction and retry once
console.error(`[pi] promptWithFallback: context limit error — attempting auto-compaction`);
const compactResult = await compactSessionContext(session);
if (!compactResult) {
console.error(`[pi] promptWithFallback: compaction unavailable — propagating original error`);
throw err;
}
console.error(`[pi] promptWithFallback: compaction succeeded (${compactResult.tokensBefore} tokens) — retrying prompt`);
try {
if (options === undefined) {
await session.prompt(prompt);
} else {
await (session.prompt as any)(prompt, options);
}
console.error(`[pi] promptWithFallback: prompt completed after auto-compaction`);
} catch (retryErr: unknown) {
const retryErrorMessage = retryErr instanceof Error ? retryErr.message : String(retryErr);
console.error(`[pi] promptWithFallback: retry after auto-compaction failed: ${retryErrorMessage}`);
throw err; // Throw original error to preserve original context
}
}
console.error(`[pi] promptWithFallback: prompt completed`);
}
/**
@@ -564,7 +595,33 @@ export async function createKbAgent(options: AgentOptions): Promise<AgentResult>
}
return;
} catch (err: any) {
if (!fallbackModel || usingFallback || !isRetryableModelSelectionError(err?.message || "")) {
const errorMessage = err?.message || "";
if (isContextLimitError(errorMessage)) {
// Context limit error — attempt auto-compaction and retry once
console.error(`[pi] promptWithFallback: context limit error — attempting auto-compaction`);
const compactResult = await compactSessionContext(session);
if (compactResult) {
console.error(`[pi] promptWithFallback: compaction succeeded (${compactResult.tokensBefore} tokens) — retrying prompt`);
try {
if (promptOptions === undefined) {
await session.prompt(prompt);
} else {
await (session.prompt as any)(prompt, promptOptions);
}
return;
} catch (retryErr: any) {
const retryErrorMessage = retryErr?.message || "";
console.error(`[pi] promptWithFallback: retry after auto-compaction failed: ${retryErrorMessage}`);
// Throw original error to preserve original context
throw err;
}
} else {
console.error(`[pi] promptWithFallback: compaction unavailable — propagating original error`);
throw err;
}
}
if (!fallbackModel || usingFallback || !isRetryableModelSelectionError(errorMessage)) {
throw err;
}
@@ -603,10 +660,39 @@ export async function createKbAgent(options: AgentOptions): Promise<AgentResult>
Object.assign(promptableSession, fallbackSession);
promptableSession.promptWithFallback = fallbackSession.promptWithFallback ?? promptableSession.promptWithFallback;
if (promptOptions === undefined) {
await fallbackSession.prompt(prompt);
} else {
await (fallbackSession.prompt as any)(prompt, promptOptions);
// Retry with fallback model, also with auto-compaction support
try {
if (promptOptions === undefined) {
await fallbackSession.prompt(prompt);
} else {
await (fallbackSession.prompt as any)(prompt, promptOptions);
}
return;
} catch (fallbackErr: any) {
const fallbackErrorMessage = fallbackErr?.message || "";
if (isContextLimitError(fallbackErrorMessage)) {
console.error(`[pi] promptWithFallback: fallback session context limit error — attempting auto-compaction`);
const compactResult = await compactSessionContext(fallbackSession);
if (compactResult) {
console.error(`[pi] promptWithFallback: fallback compaction succeeded (${compactResult.tokensBefore} tokens) — retrying`);
try {
if (promptOptions === undefined) {
await fallbackSession.prompt(prompt);
} else {
await (fallbackSession.prompt as any)(prompt, promptOptions);
}
return;
} catch (retryErr: any) {
const retryErrorMessage = retryErr?.message || "";
console.error(`[pi] promptWithFallback: fallback retry after auto-compaction failed: ${retryErrorMessage}`);
throw fallbackErr; // Throw original fallback error
}
} else {
console.error(`[pi] promptWithFallback: fallback compaction unavailable — propagating original error`);
throw fallbackErr;
}
}
throw fallbackErr;
}
}
};