agentHost: improve Agent Merge CI diagnostics (#335501)

* agentHost: improve Agent Merge CI diagnostics

Replace prefix-only CI dumps with bounded summaries and authorized, cached tail/range/search reads. Preserve true EOF completeness, redaction, cancellation, and workflow-attempt identity while keeping responses and retained evidence bounded.

Serialize concurrent reads and paginate summaries within cache capacity so follow-up evidence remains actionable without changing repair scheduling.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* agentHost: index Agent Merge CI evidence for bounded seeking

Cache sparse line-start offsets so search continuations, context excerpts, ranges, and tails do not repeatedly scan logs from the beginning. Cover 500,000-line pagination, newline-dense 16 MiB logs, checkpoint boundaries, and empty evidence.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: benibenj

src/vs/platform/agentHost/node/agentMergeCIEvidence.ts

@@ -0,0 +1,330 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { RunOnceScheduler } from '../../../base/common/async.js';
+import { VSBuffer } from '../../../base/common/buffer.js';
+import { Event } from '../../../base/common/event.js';
+import { Disposable, DisposableMap } from '../../../base/common/lifecycle.js';
+import { LRUCache } from '../../../base/common/map.js';
+import { escapeRegExpCharacters } from '../../../base/common/strings.js';
+import { generateUuid } from '../../../base/common/uuid.js';
+import { GitHubWorkflowJob, GitHubWorkflowLog } from '../../github/common/githubPullRequestMutationService.js';
+import { AgentMergeCIRequest } from './shared/agentMergeServerTools.js';
+
+export const agentMergeCIResponseBytes = 48_000;
+const evidenceLifetime = 5 * 60_000;
+const maximumEvidenceEntries = 8;
+const maximumEvidenceCharacters = 32 * 1024 * 1024;
+const excerptBytes = 6_000;
+const lineIndexStride = 1_024;
+
+export interface AgentMergeCIEvidence {
+	readonly id: string;
+	readonly scope: string;
+	readonly runAttempt: number;
+	readonly job: GitHubWorkflowJob;
+	readonly log: GitHubWorkflowLog;
+	readonly lineCount: number;
+	/** One UTF-16 offset per 1,024 lines bounds seeking without a full per-line index. */
+	readonly lineStartOffsets: Uint32Array;
+	readonly expiresAt: number;
+}
+
+export interface AgentMergeCIContinuation {
+	readonly request: AgentMergeCIRequest;
+	readonly summaryOffset?: number;
+	readonly signature?: string;
+}
+
+/** Holds only redacted, immutable evidence; authorization is rechecked by the tool before every use. */
+export class AgentMergeCIEvidenceStore extends Disposable {
+	private readonly _entries = new Map<string, AgentMergeCIEvidence>();
+	private readonly _listeners = this._register(new DisposableMap<string>());
+	private readonly _cursors = new LRUCache<string, AgentMergeCIContinuation & { scope: string; expiresAt: number }>(128);
+	private readonly _expiry = this._register(new RunOnceScheduler(() => this._prune(), evidenceLifetime));
+	private _characters = 0;
+
+	find(scope: string, jobId: string, runId: string, runAttempt: number): AgentMergeCIEvidence | undefined {
+		this._prune();
+		const entry = [...this._entries.values()].find(entry => entry.scope === scope && entry.job.id === jobId && entry.job.runId === runId && entry.runAttempt === runAttempt);
+		if (!entry) {
+			return undefined;
+		}
+		// Reused evidence must not expire while its new summary is still being assembled.
+		const refreshed = { ...entry, expiresAt: Date.now() + evidenceLifetime };
+		this._entries.delete(entry.id);
+		this._entries.set(entry.id, refreshed);
+		return refreshed;
+	}
+
+	get(id: string, scope: string): AgentMergeCIEvidence {
+		this._prune();
+		const entry = this._entries.get(id);
+		if (!entry || entry.scope !== scope) {
+			throw new Error('Invalid, expired, or unauthorized CI evidence ID. Read a new summary for the active Agent Merge turn.');
+		}
+		this._entries.delete(id);
+		this._entries.set(id, entry);
+		return entry;
+	}
+
+	canAdd(retainedIds: ReadonlySet<string>, characters = 0): boolean {
+		const retained = [...this._entries.values()].filter(entry => retainedIds.has(entry.id));
+		return retained.length < maximumEvidenceEntries
+			&& retained.reduce((total, entry) => total + entry.log.text.length, characters) <= maximumEvidenceCharacters;
+	}
+
+	/** Returns undefined when the log cannot fit without evicting evidence already advertised on this page. */
+	tryAdd(scope: string, runAttempt: number, job: GitHubWorkflowJob, log: GitHubWorkflowLog, signal: AbortSignal, retainedIds: ReadonlySet<string> = new Set()): AgentMergeCIEvidence | undefined {
+		signal.throwIfAborted();
+		if (this._store.isDisposed || log.text.length > maximumEvidenceCharacters) {
+			throw new Error('CI evidence storage is unavailable or its memory limit was exceeded.');
+		}
+		this._prune();
+		if (!this.canAdd(retainedIds, log.text.length)) {
+			return undefined;
+		}
+		while (this._entries.size >= maximumEvidenceEntries || this._characters + log.text.length > maximumEvidenceCharacters) {
+			this._delete([...this._entries.keys()].find(id => !retainedIds.has(id))!);
+		}
+		const entry: AgentMergeCIEvidence = {
+			id: generateUuid(), scope, runAttempt,
+			job: { id: job.id, runId: job.runId, name: job.name.slice(0, 200), headSha: job.headSha, runAttempt: job.runAttempt, checkRunId: job.checkRunId },
+			log: { ...log },
+			...indexLines(log.text),
+			expiresAt: Date.now() + evidenceLifetime,
+		};
+		this._entries.set(entry.id, entry);
+		this._characters += log.text.length;
+		this._listeners.set(entry.id, Event.once(Event.fromDOMEventEmitter(signal, 'abort'))(() => this._delete(entry.id)));
+		this._expiry.schedule();
+		return entry;
+	}
+
+	continue(scope: string, continuation: AgentMergeCIContinuation): { cursor: string } {
+		const cursor = generateUuid();
+		this._cursors.set(cursor, { ...continuation, scope, expiresAt: Date.now() + evidenceLifetime });
+		this._expiry.schedule();
+		return { cursor };
+	}
+
+	resolve(cursor: string, scope: string): AgentMergeCIContinuation {
+		this._prune();
+		const continuation = this._cursors.get(cursor);
+		if (!continuation || continuation.scope !== scope) {
+			throw new Error('Invalid, expired, or unauthorized CI cursor. Read a new summary for the active Agent Merge turn.');
+		}
+		return continuation;
+	}
+
+	private _delete(id: string): void {
+		const entry = this._entries.get(id);
+		if (entry) {
+			this._characters -= entry.log.text.length;
+			this._entries.delete(id);
+			this._listeners.deleteAndDispose(id);
+		}
+	}
+
+	private _prune(): void {
+		for (const entry of this._entries.values()) {
+			if (entry.expiresAt <= Date.now()) {
+				this._delete(entry.id);
+			}
+		}
+		for (const [id, cursor] of [...this._cursors]) {
+			if (cursor.expiresAt <= Date.now()) {
+				this._cursors.delete(id);
+			}
+		}
+		if (this._entries.size || this._cursors.size) {
+			this._expiry.schedule();
+		}
+	}
+
+	override dispose(): void {
+		this._entries.clear();
+		this._cursors.clear();
+		this._characters = 0;
+		super.dispose();
+	}
+}
+
+interface CILine {
+	readonly line: number;
+	readonly column: number;
+	readonly text: string;
+}
+
+export interface CIExcerpt {
+	readonly lines: readonly CILine[];
+	readonly next?: AgentMergeCIRequest;
+	readonly previous?: AgentMergeCIRequest;
+}
+
+export function ciJsonBytes(value: object): number {
+	return VSBuffer.fromString(JSON.stringify(value)).byteLength;
+}
+
+function indexLines(text: string): Pick<AgentMergeCIEvidence, 'lineCount' | 'lineStartOffsets'> {
+	const offsets: number[] = [];
+	let lineCount = 0;
+	for (let offset = 0; offset < text.length; lineCount++) {
+		if (lineCount % lineIndexStride === 0) {
+			offsets.push(offset);
+		}
+		const end = text.indexOf('\n', offset);
+		offset = end < 0 ? text.length : end + 1;
+	}
+	return { lineCount, lineStartOffsets: Uint32Array.from(offsets) };
+}
+
+function* linesInRange(entry: AgentMergeCIEvidence, first: number, last: number): Iterable<{ line: number; start: number; end: number }> {
+	const text = entry.log.text;
+	const checkpoint = Math.floor((first - 1) / lineIndexStride);
+	let line = checkpoint * lineIndexStride + 1;
+	for (let start = entry.lineStartOffsets[checkpoint] ?? text.length; start < text.length && line <= last; line++) {
+		const newline = text.indexOf('\n', start);
+		const end = newline < 0 ? text.length : newline;
+		if (line >= first) {
+			yield { line, start, end: end > start && text[end - 1] === '\r' ? end - 1 : end };
+		}
+		start = end + 1;
+	}
+}
+
+export function readCIRange(entry: AgentMergeCIEvidence, request: AgentMergeCIRequest, budget = excerptBytes): CIExcerpt {
+	const first = request.startLine ?? 1;
+	const last = Math.min(request.endLine ?? first + 199, entry.lineCount);
+	if (first > Math.max(1, entry.lineCount)) {
+		throw new Error('The requested line is outside the captured CI evidence. The total line count is unknown when complete is false.');
+	}
+	const result: CILine[] = [];
+	let remaining = budget;
+	for (const line of linesInRange(entry, first, last)) {
+		let column = line.line === first ? request.startColumn ?? 1 : 1;
+		if (column > Math.max(1, line.end - line.start)) {
+			throw new Error('The requested column is outside the captured CI line.');
+		}
+		do {
+			const text = entry.log.text.slice(line.start + column - 1, Math.min(line.end, line.start + column - 1 + 500));
+			const part = { line: line.line, column, text };
+			const bytes = ciJsonBytes(part) + 1;
+			if (bytes > remaining || result.length >= 200) {
+				return { lines: result, next: { mode: 'range', evidenceId: entry.id, startLine: line.line, startColumn: column, endLine: last } };
+			}
+			result.push(part);
+			remaining -= bytes;
+			column += text.length;
+		} while (line.start + column - 1 < line.end);
+	}
+	return { lines: result };
+}
+
+export function readCITail(entry: AgentMergeCIEvidence, lineCount = 100, budget = excerptBytes): CIExcerpt {
+	const candidates = [...linesInRange(entry, Math.max(1, entry.lineCount - lineCount + 1), entry.lineCount)];
+	const result: CILine[] = [];
+	let remaining = budget;
+	for (const line of candidates.reverse()) {
+		let end = line.end;
+		do {
+			const start = Math.max(line.start, end - 200);
+			const part = { line: line.line, column: start - line.start + 1, text: entry.log.text.slice(start, end) };
+			const bytes = ciJsonBytes(part) + 1;
+			if (bytes > remaining || result.length >= 200) {
+				return {
+					lines: result.reverse(),
+					previous: { mode: 'range', evidenceId: entry.id, startLine: Math.max(1, line.line - 199), endLine: line.line },
+				};
+			}
+			result.push(part);
+			remaining -= bytes;
+			end = start;
+		} while (end > line.start);
+	}
+	const first = result.at(-1)?.line ?? 1;
+	return {
+		lines: result.reverse(),
+		previous: first > 1 ? { mode: 'range', evidenceId: entry.id, startLine: Math.max(1, first - 200), endLine: first - 1 } : undefined,
+	};
+}
+
+export function searchCIEvidence(entry: AgentMergeCIEvidence, request: AgentMergeCIRequest) {
+	const query = new RegExp(escapeRegExpCharacters(request.query!), 'i');
+	const first = request.startLine ?? 1;
+	if (first > Math.max(1, entry.lineCount)) {
+		throw new Error('The search start line is outside the captured CI evidence.');
+	}
+	const context = request.contextLines ?? 2;
+	const matches: { line: number; excerpt: readonly CILine[]; read: AgentMergeCIRequest }[] = [];
+	let bytes = 0;
+	let scannedThrough = first - 1;
+	for (const line of linesInRange(entry, first, Math.min(entry.lineCount, first + 49_999))) {
+		if (matches.length >= 5) {
+			break;
+		}
+		const text = entry.log.text.slice(line.start, line.end);
+		const index = text.search(query);
+		if (index >= 0) {
+			const excerpt: CILine[] = [];
+			for (const surrounding of linesInRange(entry, Math.max(1, line.line - context), Math.min(entry.lineCount, line.line + context))) {
+				const column = surrounding.line === line.line ? index + 1 : 1;
+				const length = surrounding.line === line.line ? 200 : 60;
+				excerpt.push({ line: surrounding.line, column, text: entry.log.text.slice(surrounding.start + column - 1, Math.min(surrounding.end, surrounding.start + column - 1 + length)) });
+			}
+			const match = {
+				line: line.line, excerpt,
+				read: { mode: 'range' as const, evidenceId: entry.id, startLine: line.line, startColumn: index + 1, endLine: line.line },
+			};
+			const size = ciJsonBytes(match);
+			if (bytes + size > 8_000 && matches.length) {
+				break;
+			}
+			matches.push(match);
+			bytes += size;
+		}
+		scannedThrough = line.line;
+	}
+	return {
+		matches,
+		scannedThrough,
+		next: scannedThrough < entry.lineCount ? { ...request, startLine: scannedThrough + 1 } : undefined,
+	};
+}
+
+export function ciFailureExcerpt(entry: AgentMergeCIEvidence): readonly CILine[] {
+	const result: CILine[] = [];
+	for (const line of linesInRange(entry, 1, entry.lineCount)) {
+		const text = entry.log.text.slice(line.start, line.end);
+		const index = text.search(/\b(?:[1-9]\d* failing|failed|AssertionError|Error|FAIL(?:URE|ED)?)\b|##\[error\]/i);
+		if (index >= 0) {
+			const column = Math.max(1, index - 40 + 1);
+			result.push({ line: line.line, column, text: text.slice(column - 1, column - 1 + 200) });
+			if (result.length > 3) {
+				result.shift();
+			}
+		}
+	}
+	return result;
+}
+
+export function ciEvidenceMetadata(entry: AgentMergeCIEvidence) {
+	return {
+		evidenceId: entry.id,
+		runId: entry.job.runId,
+		runAttempt: entry.runAttempt,
+		jobId: entry.job.id,
+		jobHeadSha: entry.job.headSha ?? null,
+		jobRunAttempt: entry.job.runAttempt ?? null,
+		complete: !entry.log.truncated,
+		capturedLines: entry.lineCount,
+		lineNumbering: 'One-based lines and UTF-16 columns in the cached redacted text.',
+		totalLines: entry.log.truncated ? null : entry.lineCount,
+		bytesRead: entry.log.bytesRead ?? null,
+		maximumBytes: entry.log.maximumBytes ?? null,
+		terminalLimit: entry.log.truncated ? 'Download stopped before EOF. Only the captured prefix is available; the true tail and uncaptured lines are unavailable. Repeating this read cannot extend the download limit.' : null,
+		expiresAt: new Date(entry.expiresAt).toISOString(),
+	};
+}