fix(coding-agent): suppress hashline output for agents without edit tool

Hashline prefixes (LINE:HASH|content) in read/grep output exist solely to
support the hashline edit mode. Agents that don't have the edit tool
(e.g. explore, plan, reviewer) gain nothing from them — they just waste
tokens and add noise.

resolveFileDisplayMode now takes a session-like object with an optional
hasEditTool flag. When false, hashlines are suppressed regardless of
settings. ToolSession gains hasEditTool (set from toolNames in the SDK),
and AgentSession exposes it as a getter over the tool registry.

packages/coding-agent/src/sdk.ts

@@ -701,6 +701,9 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 		cwd,
 		hasUI: options.hasUI ?? false,
 		enableLsp,
+		get hasEditTool() {
+			return !options.toolNames || options.toolNames.includes("edit");
+		},
 		skipPythonPreflight: options.skipPythonPreflight,
 		contextFiles,
 		skills,

packages/coding-agent/src/session/agent-session.ts

@@ -1072,6 +1072,11 @@ export class AgentSession {
 		return this.agent.state.tools.map(t => t.name);
 	}
 
+	/** Whether the edit tool is registered in this session. */
+	get hasEditTool(): boolean {
+		return this.#toolRegistry.has("edit");
+	}
+
 	/**
 	 * Get a tool by name from the registry.
 	 */
@@ -1518,7 +1523,7 @@ export class AgentSession {
 			if (fileMentions.length > 0) {
 				const fileMentionMessages = await generateFileMentionMessages(fileMentions, this.sessionManager.getCwd(), {
 					autoResizeImages: this.settings.get("images.autoResize"),
-					useHashLines: resolveFileDisplayMode(this.settings).hashLines,
+					useHashLines: resolveFileDisplayMode(this).hashLines,
 				});
 				messages.push(...fileMentionMessages);
 			}

packages/coding-agent/src/tools/grep.ts

@@ -62,7 +62,7 @@ export class GrepTool implements AgentTool<typeof grepSchema, GrepToolDetails> {
 	readonly parameters = grepSchema;
 
 	constructor(private readonly session: ToolSession) {
-		const displayMode = resolveFileDisplayMode(session.settings);
+		const displayMode = resolveFileDisplayMode(session);
 		this.description = renderPromptTemplate(grepDescription, {
 			IS_HASHLINE_MODE: displayMode.hashLines,
 			IS_LINE_NUMBER_MODE: !displayMode.hashLines && displayMode.lineNumbers,
@@ -103,7 +103,7 @@ export class GrepTool implements AgentTool<typeof grepSchema, GrepToolDetails> {
 			const patternHasNewline = normalizedPattern.includes("\n") || normalizedPattern.includes("\\n");
 			const effectiveMultiline = multiline ?? patternHasNewline;
 
-			const useHashLines = resolveFileDisplayMode(this.session.settings).hashLines;
+			const useHashLines = resolveFileDisplayMode(this.session).hashLines;
 			const searchPath = resolveToCwd(searchDir || ".", this.session.cwd);
 			const scopePath = (() => {
 				const relative = path.relative(this.session.cwd, searchPath).replace(/\\/g, "/");

packages/coding-agent/src/tools/index.ts

@@ -119,6 +119,8 @@ export interface ToolSession {
 	promptTemplates?: PromptTemplate[];
 	/** Whether LSP integrations are enabled */
 	enableLsp?: boolean;
+	/** Whether the edit tool is available in this session (controls hashline output) */
+	hasEditTool?: boolean;
 	/** Event bus for tool/extension communication */
 	eventBus?: EventBus;
 	/** Output schema for structured completion (subagents) */

packages/coding-agent/src/tools/read.ts

@@ -544,7 +544,7 @@ export class ReadTool implements AgentTool<typeof readSchema, ReadToolDetails> {
 	readonly #autoResizeImages: boolean;
 
 	constructor(private readonly session: ToolSession) {
-		const displayMode = resolveFileDisplayMode(session.settings);
+		const displayMode = resolveFileDisplayMode(session);
 		this.#autoResizeImages = session.settings.get("images.autoResize");
 		this.description = renderPromptTemplate(readDescription, {
 			DEFAULT_MAX_LINES: String(DEFAULT_MAX_LINES),
@@ -562,7 +562,7 @@ export class ReadTool implements AgentTool<typeof readSchema, ReadToolDetails> {
 	): Promise<AgentToolResult<ReadToolDetails>> {
 		const { path: readPath, offset, limit } = params;
 
-		const displayMode = resolveFileDisplayMode(this.session.settings);
+		const displayMode = resolveFileDisplayMode(this.session);
 
 		// Handle internal URLs (agent://, skill://)
 		const internalRouter = this.session.internalRouter;
@@ -848,7 +848,7 @@ export class ReadTool implements AgentTool<typeof readSchema, ReadToolDetails> {
 	async #handleInternalUrl(url: string, offset?: number, limit?: number): Promise<AgentToolResult<ReadToolDetails>> {
 		const internalRouter = this.session.internalRouter!;
 
-		const displayMode = resolveFileDisplayMode(this.session.settings);
+		const displayMode = resolveFileDisplayMode(this.session);
 
 		// Check if URL has query extraction (agent:// only)
 		let parsed: URL;

packages/coding-agent/src/utils/file-display-mode.ts

@@ -1,25 +1,34 @@
 /**
  * Resolve line-display mode for file-like outputs (read, grep, @file mentions).
  */
-export interface FileDisplayModeSettings {
-	get(key: "readLineNumbers" | "readHashLines" | "edit.mode"): unknown;
-}
 
 export interface FileDisplayMode {
 	lineNumbers: boolean;
 	hashLines: boolean;
 }
 
-/**
- * Computes effective line display mode from settings/env.
- * Hashline mode takes precedence and implies line-addressed output everywhere.
- */
-export function resolveFileDisplayMode(settings: FileDisplayModeSettings): FileDisplayMode {
-	const hashLines =
-		settings.get("readHashLines") === true ||
-		settings.get("edit.mode") === "hashline" ||
-		Bun.env.PI_EDIT_VARIANT === "hashline";
+/** Session-like object providing settings and tool availability for display mode resolution. */
+export interface FileDisplayModeSession {
+	/** Whether the edit tool is available. Hashlines are suppressed without it. */
+	hasEditTool?: boolean;
+	settings: {
+		get(key: "readLineNumbers" | "readHashLines" | "edit.mode"): unknown;
+	};
+}
 
+/**
+ * Computes effective line display mode from session settings/env.
+ * Hashline mode takes precedence and implies line-addressed output everywhere.
+ * Hashlines are suppressed when the edit tool is not available (e.g. explore agents).
+ */
+export function resolveFileDisplayMode(session: FileDisplayModeSession): FileDisplayMode {
+	const { settings } = session;
+	const hasEditTool = session.hasEditTool ?? true;
+	const hashLines =
+		hasEditTool &&
+		(settings.get("readHashLines") === true ||
+			settings.get("edit.mode") === "hashline" ||
+			Bun.env.PI_EDIT_VARIANT === "hashline");
 	return {
 		hashLines,
 		lineNumbers: hashLines || settings.get("readLineNumbers") === true,