Implement tool result truncation with actionable notices (#134)

- read: actionable notices with offset for continuation
  - First line > 30KB: return empty + bash command suggestion
  - Hit limit: '[Showing lines X-Y of Z. Use offset=N to continue]'

- bash: tail truncation with temp file
  - Notice includes line range + temp file path
  - Edge case: last line > 30KB shows partial

- grep: pre-truncate match lines to 500 chars
  - '[... truncated]' suffix on long lines
  - Notice for match limit and line truncation

- find/ls: result/entry limit notices
  - '[N results limit reached. Use limit=M for more]'

- All notices now in text content (LLM sees them)
- TUI simplified (notices render as part of output)
- Never return partial lines (except bash edge case)

packages/ai/test/context-overflow.test.ts

@@ -118,7 +118,8 @@ describe("Context overflow error handling", () => {
 
 	describe.skipIf(!process.env.OPENAI_API_KEY)("OpenAI Completions", () => {
 		it("gpt-4o-mini - should detect overflow via isContextOverflow", async () => {
-			const model = getModel("openai", "gpt-4o-mini");
+			const model = { ...getModel("openai", "gpt-4o-mini") };
+			model.api = "openai-completions" as any;
 			const result = await testContextOverflow(model, process.env.OPENAI_API_KEY!);
 			logResult(result);
 

packages/coding-agent/docs/truncation.md

@@ -0,0 +1,235 @@
+# Tool Output Truncation
+
+## Limits
+
+- **Line limit**: 2000 lines
+- **Byte limit**: 30KB
+- **Grep line limit**: 500 chars per match line
+
+Whichever limit is hit first wins. **Never return partial lines** (except bash edge case).
+
+---
+
+## read
+
+Head truncation (first N lines). Has offset/limit params for continuation.
+
+### Scenarios
+
+**First line > 30KB:**
+```
+LLM sees:
+[Line 1 is 50KB, exceeds 30KB limit. Use bash to read: head -c 30000 path/to/file]
+
+Details:
+{ truncation: { truncated: true, truncatedBy: "bytes", outputLines: 0, ... } }
+```
+
+**Hit line limit (2000 lines, < 30KB):**
+```
+LLM sees:
+[lines 1-2000 content]
+
+[Showing lines 1-2000 of 5000. Use offset=2001 to continue]
+
+Details:
+{ truncation: { truncated: true, truncatedBy: "lines", outputLines: 2000, totalLines: 5000 } }
+```
+
+**Hit byte limit (< 2000 lines, 30KB):**
+```
+LLM sees:
+[lines 1-500 content]
+
+[Showing lines 1-500 of 5000 (30KB limit). Use offset=501 to continue]
+
+Details:
+{ truncation: { truncated: true, truncatedBy: "bytes", outputLines: 500, totalLines: 5000 } }
+```
+
+**With offset, hit line limit (e.g., offset=1000):**
+```
+LLM sees:
+[lines 1000-2999 content]
+
+[Showing lines 1000-2999 of 5000. Use offset=3000 to continue]
+
+Details:
+{ truncation: { truncatedBy: "lines", ... } }
+```
+
+**With offset, hit byte limit (e.g., offset=1000, 30KB after 500 lines):**
+```
+LLM sees:
+[lines 1000-1499 content]
+
+[Showing lines 1000-1499 of 5000 (30KB limit). Use offset=1500 to continue]
+
+Details:
+{ truncation: { truncatedBy: "bytes", outputLines: 500, ... } }
+```
+
+**With offset, first line at offset > 30KB (e.g., offset=1000, line 1000 is 50KB):**
+```
+LLM sees:
+[Line 1000 is 50KB, exceeds 30KB limit. Use bash: sed -n '1000p' file | head -c 30000]
+
+Details:
+{ truncation: { truncated: true, truncatedBy: "bytes", outputLines: 0 } }
+```
+
+---
+
+## bash
+
+Tail truncation (last N lines). Writes full output to temp file if truncated.
+
+### Scenarios
+
+**Hit line limit (2000 lines):**
+```
+LLM sees:
+[lines 48001-50000 content]
+
+[Showing lines 48001-50000 of 50000. Full output: /tmp/pi-bash-xxx.log]
+
+Details:
+{ truncation: { truncated: true, truncatedBy: "lines", outputLines: 2000, totalLines: 50000 }, fullOutputPath: "/tmp/..." }
+```
+
+**Hit byte limit (< 2000 lines, 30KB):**
+```
+LLM sees:
+[lines 49501-50000 content]
+
+[Showing lines 49501-50000 of 50000 (30KB limit). Full output: /tmp/pi-bash-xxx.log]
+
+Details:
+{ truncation: { truncatedBy: "bytes", ... }, fullOutputPath: "/tmp/..." }
+```
+
+**Last line alone > 30KB (edge case, partial OK here):**
+```
+LLM sees:
+[last 30KB of final line]
+
+[Showing last 30KB of line 50000 (line is 100KB). Full output: /tmp/pi-bash-xxx.log]
+
+Details:
+{ truncation: { truncatedBy: "bytes", lastLinePartial: true }, fullOutputPath: "/tmp/..." }
+```
+
+---
+
+## grep
+
+Head truncation. Primary limit: 100 matches. Each match line truncated to 500 chars.
+
+### Scenarios
+
+**Hit match limit (100 matches):**
+```
+LLM sees:
+file.ts:10: matching content here...
+file.ts:25: another match...
+...
+
+[100 matches limit reached. Use limit=200 for more, or refine pattern]
+
+Details:
+{ matchLimitReached: 100 }
+```
+
+**Hit byte limit (< 100 matches, 30KB):**
+```
+LLM sees:
+[matches that fit in 30KB]
+
+[30KB limit reached (50 of 100+ matches shown)]
+
+Details:
+{ truncation: { truncatedBy: "bytes", ... } }
+```
+
+**Match lines truncated (any line > 500 chars):**
+```
+LLM sees:
+file.ts:10: very long matching content that exceeds 500 chars gets cut off here... [truncated]
+file.ts:25: normal match
+
+[Some lines truncated to 500 chars. Use read tool to see full lines]
+
+Details:
+{ linesTruncated: true }
+```
+
+---
+
+## find
+
+Head truncation. Primary limit: 1000 results. File paths only (never > 30KB each).
+
+### Scenarios
+
+**Hit result limit (1000 results):**
+```
+LLM sees:
+src/file1.ts
+src/file2.ts
+[998 more paths]
+
+[1000 results limit reached. Use limit=2000 for more, or refine pattern]
+
+Details:
+{ resultLimitReached: 1000 }
+```
+
+**Hit byte limit (unlikely, < 1000 results, 30KB):**
+```
+LLM sees:
+[paths that fit]
+
+[30KB limit reached]
+
+Details:
+{ truncation: { truncatedBy: "bytes", ... } }
+```
+
+---
+
+## ls
+
+Head truncation. Primary limit: 500 entries. Entry names only (never > 30KB each).
+
+### Scenarios
+
+**Hit entry limit (500 entries):**
+```
+LLM sees:
+.gitignore
+README.md
+src/
+[497 more entries]
+
+[500 entries limit reached. Use limit=1000 for more]
+
+Details:
+{ entryLimitReached: 500 }
+```
+
+**Hit byte limit (unlikely):**
+```
+LLM sees:
+[entries that fit]
+
+[30KB limit reached]
+
+Details:
+{ truncation: { truncatedBy: "bytes", ... } }
+```
+
+---
+
+## TUI Display
+
+`tool-execution.ts` reads `details.truncation` and related fields to display truncation notices in warning color. The LLM text content and TUI display show the same information.

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

@@ -6,7 +6,7 @@ import type { AgentTool } from "@mariozechner/pi-ai";
 import { Type } from "@sinclair/typebox";
 import { spawn, spawnSync } from "child_process";
 import { SettingsManager } from "../settings-manager.js";
-import { DEFAULT_MAX_BYTES, DEFAULT_MAX_LINES, type TruncationResult, truncateTail } from "./truncate.js";
+import { DEFAULT_MAX_BYTES, DEFAULT_MAX_LINES, formatSize, type TruncationResult, truncateTail } from "./truncate.js";
 
 let cachedShellConfig: { shell: string; args: string[] } | null = null;
 
@@ -256,11 +256,26 @@ export const bashTool: AgentTool<typeof bashSchema> = {
 
 				// Build details with truncation info
 				let details: BashToolDetails | undefined;
+
 				if (truncation.truncated) {
 					details = {
 						truncation,
 						fullOutputPath: tempFilePath,
 					};
+
+					// Build actionable notice
+					const startLine = truncation.totalLines - truncation.outputLines + 1;
+					const endLine = truncation.totalLines;
+
+					if (truncation.lastLinePartial) {
+						// Edge case: last line alone > 30KB
+						const lastLineSize = formatSize(Buffer.byteLength(fullOutput.split("\n").pop() || "", "utf-8"));
+						outputText += `\n\n[Showing last ${formatSize(truncation.outputBytes)} of line ${endLine} (line is ${lastLineSize}). Full output: ${tempFilePath}]`;
+					} else if (truncation.truncatedBy === "lines") {
+						outputText += `\n\n[Showing lines ${startLine}-${endLine} of ${truncation.totalLines}. Full output: ${tempFilePath}]`;
+					} else {
+						outputText += `\n\n[Showing lines ${startLine}-${endLine} of ${truncation.totalLines} (${formatSize(DEFAULT_MAX_BYTES)} limit). Full output: ${tempFilePath}]`;
+					}
 				}
 
 				if (code !== 0 && code !== null) {

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

@@ -6,7 +6,7 @@ import { globSync } from "glob";
 import { homedir } from "os";
 import path from "path";
 import { ensureTool } from "../tools-manager.js";
-import { DEFAULT_MAX_BYTES, type TruncationResult, truncateHead } from "./truncate.js";
+import { DEFAULT_MAX_BYTES, formatSize, type TruncationResult, truncateHead } from "./truncate.js";
 
 /**
  * Expand ~ to home directory
@@ -160,25 +160,39 @@ export const findTool: AgentTool<typeof findSchema> = {
 						relativized.push(relativePath);
 					}
 
-					const rawOutput = relativized.join("\n");
-					let details: FindToolDetails | undefined;
-
 					// Check if we hit the result limit
-					const hitResultLimit = relativized.length >= effectiveLimit;
+					const resultLimitReached = relativized.length >= effectiveLimit;
 
-					// Apply byte truncation
+					// Apply byte truncation (no line limit since we already have result limit)
+					const rawOutput = relativized.join("\n");
 					const truncation = truncateHead(rawOutput, { maxLines: Number.MAX_SAFE_INTEGER });
-					const resultOutput = truncation.content;
 
-					// Include truncation info in details (result limit or byte limit)
+					let resultOutput = truncation.content;
-					if (hitResultLimit || truncation.truncated) {
+					const details: FindToolDetails = {};
-						details = {
+
-							truncation: truncation.truncated ? truncation : undefined,
+					// Build notices
-							resultLimitReached: hitResultLimit ? effectiveLimit : undefined,
+					const notices: string[] = [];
-						};
+
+					if (resultLimitReached) {
+						notices.push(
+							`${effectiveLimit} results limit reached. Use limit=${effectiveLimit * 2} for more, or refine pattern`,
+						);
+						details.resultLimitReached = effectiveLimit;
 					}
 
-					resolve({ content: [{ type: "text", text: resultOutput }], details });
+					if (truncation.truncated) {
+						notices.push(`${formatSize(DEFAULT_MAX_BYTES)} limit reached`);
+						details.truncation = truncation;
+					}
+
+					if (notices.length > 0) {
+						resultOutput += `\n\n[${notices.join(". ")}]`;
+					}
+
+					resolve({
+						content: [{ type: "text", text: resultOutput }],
+						details: Object.keys(details).length > 0 ? details : undefined,
+					});
 				} catch (e: any) {
 					signal?.removeEventListener("abort", onAbort);
 					reject(e);

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

@@ -6,7 +6,14 @@ import { readFileSync, type Stats, statSync } from "fs";
 import { homedir } from "os";
 import path from "path";
 import { ensureTool } from "../tools-manager.js";
-import { DEFAULT_MAX_BYTES, type TruncationResult, truncateHead } from "./truncate.js";
+import {
+	DEFAULT_MAX_BYTES,
+	formatSize,
+	GREP_MAX_LINE_LENGTH,
+	type TruncationResult,
+	truncateHead,
+	truncateLine,
+} from "./truncate.js";
 
 /**
  * Expand ~ to home directory
@@ -40,12 +47,13 @@ const DEFAULT_LIMIT = 100;
 interface GrepToolDetails {
 	truncation?: TruncationResult;
 	matchLimitReached?: number;
+	linesTruncated?: boolean;
 }
 
 export const grepTool: AgentTool<typeof grepSchema> = {
 	name: "grep",
 	label: "grep",
-	description: `Search file contents for a pattern. Returns matching lines with file paths and line numbers. Respects .gitignore. Output is truncated to ${DEFAULT_LIMIT} matches or ${DEFAULT_MAX_BYTES / 1024}KB (whichever is hit first).`,
+	description: `Search file contents for a pattern. Returns matching lines with file paths and line numbers. Respects .gitignore. Output is truncated to ${DEFAULT_LIMIT} matches or ${DEFAULT_MAX_BYTES / 1024}KB (whichever is hit first). Long lines are truncated to ${GREP_MAX_LINE_LENGTH} chars.`,
 	parameters: grepSchema,
 	execute: async (
 		_toolCallId: string,
@@ -148,7 +156,8 @@ export const grepTool: AgentTool<typeof grepSchema> = {
 					const rl = createInterface({ input: child.stdout });
 					let stderr = "";
 					let matchCount = 0;
-					let truncated = false;
+					let matchLimitReached = false;
+					let linesTruncated = false;
 					let aborted = false;
 					let killedDueToLimit = false;
 					const outputLines: string[] = [];
@@ -176,7 +185,7 @@ export const grepTool: AgentTool<typeof grepSchema> = {
 						stderr += chunk.toString();
 					});
 
-					const formatBlock = (filePath: string, lineNumber: number) => {
+					const formatBlock = (filePath: string, lineNumber: number): string[] => {
 						const relativePath = formatPath(filePath);
 						const lines = getFileLines(filePath);
 						if (!lines.length) {
@@ -192,10 +201,16 @@ export const grepTool: AgentTool<typeof grepSchema> = {
 							const sanitized = lineText.replace(/\r/g, "");
 							const isMatchLine = current === lineNumber;
 
+							// Truncate long lines
+							const { text: truncatedText, wasTruncated } = truncateLine(sanitized);
+							if (wasTruncated) {
+								linesTruncated = true;
+							}
+
 							if (isMatchLine) {
-								block.push(`${relativePath}:${current}: ${sanitized}`);
+								block.push(`${relativePath}:${current}: ${truncatedText}`);
 							} else {
-								block.push(`${relativePath}-${current}- ${sanitized}`);
+								block.push(`${relativePath}-${current}- ${truncatedText}`);
 							}
 						}
 
@@ -224,7 +239,7 @@ export const grepTool: AgentTool<typeof grepSchema> = {
 							}
 
 							if (matchCount >= effectiveLimit) {
-								truncated = true;
+								matchLimitReached = true;
 								stopChild(true);
 							}
 						}
@@ -256,22 +271,45 @@ export const grepTool: AgentTool<typeof grepSchema> = {
 							return;
 						}
 
-						// Apply byte truncation
+						// Apply byte truncation (no line limit since we already have match limit)
 						const rawOutput = outputLines.join("\n");
 						const truncation = truncateHead(rawOutput, { maxLines: Number.MAX_SAFE_INTEGER });
 
-						const output = truncation.content;
+						let output = truncation.content;
-						let details: GrepToolDetails | undefined;
+						const details: GrepToolDetails = {};
 
-						// Include truncation info in details (match limit or byte limit)
+						// Build notices
-						if (truncated || truncation.truncated) {
+						const notices: string[] = [];
-							details = {
+
-								truncation: truncation.truncated ? truncation : undefined,
+						if (matchLimitReached) {
-								matchLimitReached: truncated ? effectiveLimit : undefined,
+							notices.push(
-							};
+								`${effectiveLimit} matches limit reached. Use limit=${effectiveLimit * 2} for more, or refine pattern`,
+							);
+							details.matchLimitReached = effectiveLimit;
 						}
 
-						settle(() => resolve({ content: [{ type: "text", text: output }], details }));
+						if (truncation.truncated) {
+							notices.push(`${formatSize(DEFAULT_MAX_BYTES)} limit reached`);
+							details.truncation = truncation;
+						}
+
+						if (linesTruncated) {
+							notices.push(
+								`Some lines truncated to ${GREP_MAX_LINE_LENGTH} chars. Use read tool to see full lines`,
+							);
+							details.linesTruncated = true;
+						}
+
+						if (notices.length > 0) {
+							output += `\n\n[${notices.join(". ")}]`;
+						}
+
+						settle(() =>
+							resolve({
+								content: [{ type: "text", text: output }],
+								details: Object.keys(details).length > 0 ? details : undefined,
+							}),
+						);
 					});
 				} catch (err) {
 					settle(() => reject(err as Error));

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

@@ -3,7 +3,7 @@ import { Type } from "@sinclair/typebox";
 import { existsSync, readdirSync, statSync } from "fs";
 import { homedir } from "os";
 import nodePath from "path";
-import { DEFAULT_MAX_BYTES, type TruncationResult, truncateHead } from "./truncate.js";
+import { DEFAULT_MAX_BYTES, formatSize, type TruncationResult, truncateHead } from "./truncate.js";
 
 /**
  * Expand ~ to home directory
@@ -76,11 +76,11 @@ export const lsTool: AgentTool<typeof lsSchema> = {
 
 				// Format entries with directory indicators
 				const results: string[] = [];
-				let truncated = false;
+				let entryLimitReached = false;
 
 				for (const entry of entries) {
 					if (results.length >= effectiveLimit) {
-						truncated = true;
+						entryLimitReached = true;
 						break;
 					}
 
@@ -107,22 +107,34 @@ export const lsTool: AgentTool<typeof lsSchema> = {
 					return;
 				}
 
+				// Apply byte truncation (no line limit since we already have entry limit)
 				const rawOutput = results.join("\n");
-				let details: LsToolDetails | undefined;
-
-				// Apply byte truncation
 				const truncation = truncateHead(rawOutput, { maxLines: Number.MAX_SAFE_INTEGER });
-				const output = truncation.content;
 
-				// Include truncation info in details (entry limit or byte limit)
+				let output = truncation.content;
-				if (truncated || truncation.truncated) {
+				const details: LsToolDetails = {};
-					details = {
+
-						truncation: truncation.truncated ? truncation : undefined,
+				// Build notices
-						entryLimitReached: truncated ? effectiveLimit : undefined,
+				const notices: string[] = [];
-					};
+
+				if (entryLimitReached) {
+					notices.push(`${effectiveLimit} entries limit reached. Use limit=${effectiveLimit * 2} for more`);
+					details.entryLimitReached = effectiveLimit;
 				}
 
-				resolve({ content: [{ type: "text", text: output }], details });
+				if (truncation.truncated) {
+					notices.push(`${formatSize(DEFAULT_MAX_BYTES)} limit reached`);
+					details.truncation = truncation;
+				}
+
+				if (notices.length > 0) {
+					output += `\n\n[${notices.join(". ")}]`;
+				}
+
+				resolve({
+					content: [{ type: "text", text: output }],
+					details: Object.keys(details).length > 0 ? details : undefined,
+				});
 			} catch (e: any) {
 				signal?.removeEventListener("abort", onAbort);
 				reject(e);

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

@@ -4,7 +4,7 @@ import { Type } from "@sinclair/typebox";
 import { constants } from "fs";
 import { access, readFile } from "fs/promises";
 import { extname, resolve as resolvePath } from "path";
-import { DEFAULT_MAX_BYTES, DEFAULT_MAX_LINES, type TruncationResult, truncateHead } from "./truncate.js";
+import { DEFAULT_MAX_BYTES, DEFAULT_MAX_LINES, formatSize, type TruncationResult, truncateHead } from "./truncate.js";
 
 /**
  * Expand ~ to home directory
@@ -108,43 +108,66 @@ export const readTool: AgentTool<typeof readSchema> = {
 						} else {
 							// Read as text
 							const textContent = await readFile(absolutePath, "utf-8");
-							const lines = textContent.split("\n");
+							const allLines = textContent.split("\n");
+							const totalFileLines = allLines.length;
 
 							// Apply offset if specified (1-indexed to 0-indexed)
 							const startLine = offset ? Math.max(0, offset - 1) : 0;
+							const startLineDisplay = startLine + 1; // For display (1-indexed)
 
 							// Check if offset is out of bounds
-							if (startLine >= lines.length) {
+							if (startLine >= allLines.length) {
-								throw new Error(`Offset ${offset} is beyond end of file (${lines.length} lines total)`);
+								throw new Error(`Offset ${offset} is beyond end of file (${allLines.length} lines total)`);
 							}
 
 							// If limit is specified by user, use it; otherwise we'll let truncateHead decide
 							let selectedContent: string;
+							let userLimitedLines: number | undefined;
 							if (limit !== undefined) {
-								const endLine = Math.min(startLine + limit, lines.length);
+								const endLine = Math.min(startLine + limit, allLines.length);
-								selectedContent = lines.slice(startLine, endLine).join("\n");
+								selectedContent = allLines.slice(startLine, endLine).join("\n");
+								userLimitedLines = endLine - startLine;
 							} else {
-								selectedContent = lines.slice(startLine).join("\n");
+								selectedContent = allLines.slice(startLine).join("\n");
 							}
 
 							// Apply truncation (respects both line and byte limits)
 							const truncation = truncateHead(selectedContent);
 
-							let outputText = truncation.content;
+							let outputText: string;
 
-							// Add continuation hint if there's more content after our selection
+							if (truncation.firstLineExceedsLimit) {
-							// (only relevant when user specified limit and there's more in the file)
+								// First line at offset exceeds 30KB - tell model to use bash
-							if (limit !== undefined && startLine + limit < lines.length && !truncation.truncated) {
+								const firstLineSize = formatSize(Buffer.byteLength(allLines[startLine], "utf-8"));
-								const remaining = lines.length - (startLine + limit);
+								outputText = `[Line ${startLineDisplay} is ${firstLineSize}, exceeds ${formatSize(DEFAULT_MAX_BYTES)} limit. Use bash: sed -n '${startLineDisplay}p' ${path} | head -c ${DEFAULT_MAX_BYTES}]`;
-								outputText += `\n\n[${remaining} more lines in file. Use offset=${startLine + limit + 1} to continue]`;
+								details = { truncation };
+							} else if (truncation.truncated) {
+								// Truncation occurred - build actionable notice
+								const endLineDisplay = startLineDisplay + truncation.outputLines - 1;
+								const nextOffset = endLineDisplay + 1;
+
+								outputText = truncation.content;
+
+								if (truncation.truncatedBy === "lines") {
+									outputText += `\n\n[Showing lines ${startLineDisplay}-${endLineDisplay} of ${totalFileLines}. Use offset=${nextOffset} to continue]`;
+								} else {
+									outputText += `\n\n[Showing lines ${startLineDisplay}-${endLineDisplay} of ${totalFileLines} (${formatSize(DEFAULT_MAX_BYTES)} limit). Use offset=${nextOffset} to continue]`;
+								}
+								details = { truncation };
+							} else if (userLimitedLines !== undefined && startLine + userLimitedLines < allLines.length) {
+								// User specified limit, there's more content, but no truncation
+								const endLineDisplay = startLineDisplay + userLimitedLines - 1;
+								const remaining = allLines.length - (startLine + userLimitedLines);
+								const nextOffset = startLine + userLimitedLines + 1;
+
+								outputText = truncation.content;
+								outputText += `\n\n[${remaining} more lines in file. Use offset=${nextOffset} to continue]`;
+							} else {
+								// No truncation, no user limit exceeded
+								outputText = truncation.content;
 							}
 
 							content = [{ type: "text", text: outputText }];
-
-							// Include truncation info in details if truncation occurred
-							if (truncation.truncated) {
-								details = { truncation };
-							}
 						}
 
 						// Check if aborted after reading

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

@@ -4,10 +4,13 @@
  * Truncation is based on two independent limits - whichever is hit first wins:
  * - Line limit (default: 2000 lines)
  * - Byte limit (default: 30KB)
+ *
+ * Never returns partial lines (except bash tail truncation edge case).
  */
 
 export const DEFAULT_MAX_LINES = 2000;
 export const DEFAULT_MAX_BYTES = 30 * 1024; // 30KB
+export const GREP_MAX_LINE_LENGTH = 500; // Max chars per grep match line
 
 export interface TruncationResult {
 	/** The truncated content */
@@ -20,12 +23,14 @@ export interface TruncationResult {
 	totalLines: number;
 	/** Total number of bytes in the original content */
 	totalBytes: number;
-	/** Number of lines in the truncated output */
+	/** Number of complete lines in the truncated output */
 	outputLines: number;
 	/** Number of bytes in the truncated output */
 	outputBytes: number;
-	/** Human-readable truncation notice (empty if not truncated) */
+	/** Whether the last line was partially truncated (only for tail truncation edge case) */
-	notice: string;
+	lastLinePartial: boolean;
+	/** Whether the first line exceeded the byte limit (for head truncation) */
+	firstLineExceedsLimit: boolean;
 }
 
 export interface TruncationOptions {
@@ -38,7 +43,7 @@ export interface TruncationOptions {
 /**
  * Format bytes as human-readable size.
  */
-function formatSize(bytes: number): string {
+export function formatSize(bytes: number): string {
 	if (bytes < 1024) {
 		return `${bytes}B`;
 	} else if (bytes < 1024 * 1024) {
@@ -48,31 +53,12 @@ function formatSize(bytes: number): string {
 	}
 }
 
-/**
- * Generate a truncation notice.
- */
-function makeNotice(
-	direction: "head" | "tail",
-	truncatedBy: "lines" | "bytes",
-	totalLines: number,
-	totalBytes: number,
-	outputLines: number,
-	outputBytes: number,
-): string {
-	const totalSize = formatSize(totalBytes);
-	const outputSize = formatSize(outputBytes);
-	const directionText = direction === "head" ? "first" : "last";
-
-	if (truncatedBy === "lines") {
-		return `[Truncated: ${totalLines} lines / ${totalSize} total, showing ${directionText} ${outputLines} lines]`;
-	} else {
-		return `[Truncated: ${totalLines} lines / ${totalSize} total, showing ${directionText} ${outputSize}]`;
-	}
-}
-
 /**
  * Truncate content from the head (keep first N lines/bytes).
  * Suitable for file reads where you want to see the beginning.
+ *
+ * Never returns partial lines. If first line exceeds byte limit,
+ * returns empty content with firstLineExceedsLimit=true.
  */
 export function truncateHead(content: string, options: TruncationOptions = {}): TruncationResult {
 	const maxLines = options.maxLines ?? DEFAULT_MAX_LINES;
@@ -92,11 +78,28 @@ export function truncateHead(content: string, options: TruncationOptions = {}):
 			totalBytes,
 			outputLines: totalLines,
 			outputBytes: totalBytes,
-			notice: "",
+			lastLinePartial: false,
+			firstLineExceedsLimit: false,
 		};
 	}
 
-	// Determine which limit we'll hit first
+	// Check if first line alone exceeds byte limit
+	const firstLineBytes = Buffer.byteLength(lines[0], "utf-8");
+	if (firstLineBytes > maxBytes) {
+		return {
+			content: "",
+			truncated: true,
+			truncatedBy: "bytes",
+			totalLines,
+			totalBytes,
+			outputLines: 0,
+			outputBytes: 0,
+			lastLinePartial: false,
+			firstLineExceedsLimit: true,
+		};
+	}
+
+	// Collect complete lines that fit
 	const outputLinesArr: string[] = [];
 	let outputBytesCount = 0;
 	let truncatedBy: "lines" | "bytes" = "lines";
@@ -107,12 +110,6 @@ export function truncateHead(content: string, options: TruncationOptions = {}):
 
 		if (outputBytesCount + lineBytes > maxBytes) {
 			truncatedBy = "bytes";
-			// If this is the first line and it alone exceeds maxBytes, include partial
-			if (i === 0) {
-				const truncatedLine = truncateStringToBytes(line, maxBytes);
-				outputLinesArr.push(truncatedLine);
-				outputBytesCount = Buffer.byteLength(truncatedLine, "utf-8");
-			}
 			break;
 		}
 
@@ -136,13 +133,16 @@ export function truncateHead(content: string, options: TruncationOptions = {}):
 		totalBytes,
 		outputLines: outputLinesArr.length,
 		outputBytes: finalOutputBytes,
-		notice: makeNotice("head", truncatedBy, totalLines, totalBytes, outputLinesArr.length, finalOutputBytes),
+		lastLinePartial: false,
+		firstLineExceedsLimit: false,
 	};
 }
 
 /**
  * Truncate content from the tail (keep last N lines/bytes).
  * Suitable for bash output where you want to see the end (errors, final results).
+ *
+ * May return partial first line if the last line of original content exceeds byte limit.
  */
 export function truncateTail(content: string, options: TruncationOptions = {}): TruncationResult {
 	const maxLines = options.maxLines ?? DEFAULT_MAX_LINES;
@@ -162,7 +162,8 @@ export function truncateTail(content: string, options: TruncationOptions = {}):
 			totalBytes,
 			outputLines: totalLines,
 			outputBytes: totalBytes,
-			notice: "",
+			lastLinePartial: false,
+			firstLineExceedsLimit: false,
 		};
 	}
 
@@ -170,6 +171,7 @@ export function truncateTail(content: string, options: TruncationOptions = {}):
 	const outputLinesArr: string[] = [];
 	let outputBytesCount = 0;
 	let truncatedBy: "lines" | "bytes" = "lines";
+	let lastLinePartial = false;
 
 	for (let i = lines.length - 1; i >= 0 && outputLinesArr.length < maxLines; i--) {
 		const line = lines[i];
@@ -177,12 +179,13 @@ export function truncateTail(content: string, options: TruncationOptions = {}):
 
 		if (outputBytesCount + lineBytes > maxBytes) {
 			truncatedBy = "bytes";
-			// If this is the first line we're adding and it alone exceeds maxBytes, include partial
+			// Edge case: if we haven't added ANY lines yet and this line exceeds maxBytes,
+			// take the end of the line (partial)
 			if (outputLinesArr.length === 0) {
-				// Take the end of the line
 				const truncatedLine = truncateStringToBytesFromEnd(line, maxBytes);
 				outputLinesArr.unshift(truncatedLine);
 				outputBytesCount = Buffer.byteLength(truncatedLine, "utf-8");
+				lastLinePartial = true;
 			}
 			break;
 		}
@@ -207,29 +210,11 @@ export function truncateTail(content: string, options: TruncationOptions = {}):
 		totalBytes,
 		outputLines: outputLinesArr.length,
 		outputBytes: finalOutputBytes,
-		notice: makeNotice("tail", truncatedBy, totalLines, totalBytes, outputLinesArr.length, finalOutputBytes),
+		lastLinePartial,
+		firstLineExceedsLimit: false,
 	};
 }
 
-/**
- * Truncate a string to fit within a byte limit (from the start).
- * Handles multi-byte UTF-8 characters correctly.
- */
-function truncateStringToBytes(str: string, maxBytes: number): string {
-	const buf = Buffer.from(str, "utf-8");
-	if (buf.length <= maxBytes) {
-		return str;
-	}
-
-	// Find a valid UTF-8 boundary
-	let end = maxBytes;
-	while (end > 0 && (buf[end] & 0xc0) === 0x80) {
-		end--;
-	}
-
-	return buf.slice(0, end).toString("utf-8");
-}
-
 /**
  * Truncate a string to fit within a byte limit (from the end).
  * Handles multi-byte UTF-8 characters correctly.
@@ -250,3 +235,17 @@ function truncateStringToBytesFromEnd(str: string, maxBytes: number): string {
 
 	return buf.slice(start).toString("utf-8");
 }
+
+/**
+ * Truncate a single line to max characters, adding [truncated] suffix.
+ * Used for grep match lines.
+ */
+export function truncateLine(
+	line: string,
+	maxChars: number = GREP_MAX_LINE_LENGTH,
+): { text: string; wasTruncated: boolean } {
+	if (line.length <= maxChars) {
+		return { text: line, wasTruncated: false };
+	}
+	return { text: line.slice(0, maxChars) + "... [truncated]", wasTruncated: true };
+}

packages/coding-agent/src/tui/tool-execution.ts

@@ -128,15 +128,7 @@ export class ToolExecutionComponent extends Container {
 					}
 				}
 
-				// Show truncation notice at the bottom in warning color if present in details
+				// Truncation notice is now in the text content itself, TUI just shows it
-				const truncation = this.result.details?.truncation;
-				const fullOutputPath = this.result.details?.fullOutputPath;
-				if (truncation?.truncated) {
-					if (fullOutputPath) {
-						text += "\n" + theme.fg("warning", `[Full output: ${fullOutputPath}]`);
-					}
-					text += "\n" + theme.fg("warning", truncation.notice);
-				}
 			}
 		} else if (this.toolName === "read") {
 			const path = shortenPath(this.args?.file_path || this.args?.path || "");
@@ -166,11 +158,7 @@ export class ToolExecutionComponent extends Container {
 					text += theme.fg("toolOutput", `\n... (${remaining} more lines)`);
 				}
 
-				// Show truncation notice at the bottom in warning color if present in details
+				// Truncation notice is now in the text content itself
-				const truncation = this.result.details?.truncation;
-				if (truncation?.truncated) {
-					text += "\n" + theme.fg("warning", truncation.notice);
-				}
 			}
 		} else if (this.toolName === "write") {
 			const path = shortenPath(this.args?.file_path || this.args?.path || "");
@@ -249,15 +237,7 @@ export class ToolExecutionComponent extends Container {
 					}
 				}
 
-				// Show truncation notice from details
+				// Truncation notice is now in the text content itself
-				const entryLimit = this.result.details?.entryLimitReached;
-				const truncation = this.result.details?.truncation;
-				if (entryLimit) {
-					text += "\n" + theme.fg("warning", `[Truncated: ${entryLimit} entries limit reached]`);
-				}
-				if (truncation?.truncated) {
-					text += "\n" + theme.fg("warning", truncation.notice);
-				}
 			}
 		} else if (this.toolName === "find") {
 			const pattern = this.args?.pattern || "";
@@ -287,15 +267,7 @@ export class ToolExecutionComponent extends Container {
 					}
 				}
 
-				// Show truncation notice from details
+				// Truncation notice is now in the text content itself
-				const resultLimit = this.result.details?.resultLimitReached;
-				const truncation = this.result.details?.truncation;
-				if (resultLimit) {
-					text += "\n" + theme.fg("warning", `[Truncated: ${resultLimit} results limit reached]`);
-				}
-				if (truncation?.truncated) {
-					text += "\n" + theme.fg("warning", truncation.notice);
-				}
 			}
 		} else if (this.toolName === "grep") {
 			const pattern = this.args?.pattern || "";
@@ -329,15 +301,7 @@ export class ToolExecutionComponent extends Container {
 					}
 				}
 
-				// Show truncation notice from details
+				// Truncation notice is now in the text content itself
-				const matchLimit = this.result.details?.matchLimitReached;
-				const truncation = this.result.details?.truncation;
-				if (matchLimit) {
-					text += "\n" + theme.fg("warning", `[Truncated: ${matchLimit} matches limit reached]`);
-				}
-				if (truncation?.truncated) {
-					text += "\n" + theme.fg("warning", truncation.notice);
-				}
 			}
 		} else {
 			// Generic tool