feat(coding-agent): made hashline seen-line guard opt-in via edit.enforceSeenLines

- Added the `enforceSeenLines` option to hashline `PatcherOptions` (defaults `true`); the seen-line guard in `Patcher` now runs only when enabled.
- Added the `edit.enforceSeenLines` coding-agent setting (default off) and wired it through `edit/hashline/execute.ts` into the `Patcher`.
- Stopped `file-snapshot-store` excluding column-clipped (>512-char) lines from a snapshot's seen set, so single-line edits on long lines apply without a full-width re-read.
- Updated `seen-line-guard` tests and the hashline/coding-agent changelogs.

packages/coding-agent/CHANGELOG.md

@@ -11,11 +11,13 @@
 - Changed the default `astGrep.enabled` setting to `false`
 - Batched todo operations with real tool calls to prevent solo todo turns and extra round trips
 
+- Added the `edit.enforceSeenLines` setting (default off) to gate the hashline seen-line guard. When off, hashline tags validate on content hash alone and any anchor into the tagged content applies; when on, edits anchored on lines a prior `read`/`grep` never displayed are rejected.
 ### Fixed
 
 - Fixed Bash internal URLs remaining unresolved when used as unquoted arguments inside command substitutions ([#5535](https://github.com/can1357/oh-my-pi/issues/5535)).
 - Fixed the built-in `fd` printing `fd: Broken pipe (os error 32)` when a downstream pipeline reader exited early (e.g. `fd … | head`); it now exits silently with 141 (128+SIGPIPE), matching real fd.
 - Fixed prewalk repeatedly continuing after a bash-only task such as `commit` had already completed ([#5551](https://github.com/can1357/oh-my-pi/issues/5551)).
+- Made the hashline seen-line guard opt-in and off by default (see `edit.enforceSeenLines`), and stopped excluding column-clipped (>512-char) lines from a snapshot's seen set: a displayed line now counts as seen even when its display was column-truncated, so single-line edits on long lines found via `read`/`grep` apply without a separate full-width re-read.
 - Fixed the Bash tool hanging when in-process commands read process substitution operands such as `<(cmd)` ([#5557](https://github.com/can1357/oh-my-pi/issues/5557)).
 - Fixed `/share` and `/export` web views rendering inline Markdown inside list items as literal text ([#5567](https://github.com/can1357/oh-my-pi/issues/5567)).
 

packages/coding-agent/src/config/settings-schema.ts

@@ -3023,6 +3023,17 @@ export const SETTINGS_SCHEMA = {
 		},
 	},
 
+	"edit.enforceSeenLines": {
+		type: "boolean",
+		default: false,
+		ui: {
+			tab: "files",
+			group: "Editing",
+			label: "Enforce Seen-Line Guard",
+			description: "Reject edits anchored on lines a prior read/search never displayed in full",
+		},
+	},
+
 	readLineNumbers: {
 		type: "boolean",
 		default: false,

packages/coding-agent/src/edit/file-snapshot-store.ts

@@ -131,27 +131,18 @@ export function recordSeenLines(
 }
 
 /**
- * Attach the lines a read displayed to the snapshot it minted, so the patcher
- * can reject edits anchored on lines the model never saw. Best-effort: a no-op
- * when the body has no numbered rows or the snapshot already aged out. `tag`
- * must be the tag returned when this exact content was recorded.
- *
- * `excludedLines` prunes 1-indexed line numbers whose displayed text was
- * column-truncated (or otherwise not shown in full). A column-clipped row
- * still carries a `NN:` prefix — the parser sees the number and would
- * otherwise mark the line "seen" even though only its prefix ever reached
- * the model. Producers that apply per-line column truncation MUST supply
- * the clipped line set so the patcher's seen-line guard keeps rejecting
- * edits against those lines until a full-width read of them occurs.
+ * Attach the lines a read displayed to the snapshot it minted, so the patcher's
+ * (opt-in) seen-line guard can reject edits anchored on lines the model never
+ * saw. Best-effort: a no-op when the body has no numbered rows or the snapshot
+ * already aged out. `tag` must be the tag returned when this exact content was
+ * recorded. Every displayed `NN:` row counts as seen, including column-clipped
+ * rows — the guard no longer distinguishes full-width from truncated display.
  */
 export function recordSeenLinesFromBody(
 	session: FileSnapshotStoreOwner,
 	absolutePath: string,
 	tag: string,
 	body: string,
-	excludedLines?: ReadonlySet<number>,
 ): void {
-	const parsed = parseSeenLinesFromHashlineBody(body);
-	const filtered = excludedLines && excludedLines.size > 0 ? parsed.filter(line => !excludedLines.has(line)) : parsed;
-	recordSeenLines(session, absolutePath, tag, filtered);
+	recordSeenLines(session, absolutePath, tag, parseSeenLinesFromHashlineBody(body));
 }

packages/coding-agent/src/edit/hashline/execute.ts

@@ -210,7 +210,8 @@ export async function executeHashlineSingle(
 		batchRequest: options.batchRequest,
 	});
 	const snapshots = getFileSnapshotStore(options.session);
-	const patcher = new Patcher({ fs, snapshots, blockResolver: nativeBlockResolver });
+	const enforceSeenLines = options.session.settings.get("edit.enforceSeenLines");
+	const patcher = new Patcher({ fs, snapshots, blockResolver: nativeBlockResolver, enforceSeenLines });
 
 	// Single-section fast path: prepare, commit, render.
 	const inputHash = hashPatchInput(options.input);

packages/coding-agent/test/edit/seen-line-guard.test.ts

@@ -19,7 +19,7 @@ function createSession(cwd: string): ToolSession {
 		getSessionSpawns: () => "*",
 		getArtifactsDir: () => path.join(cwd, "artifacts"),
 		allocateOutputArtifact: async () => ({ id: "artifact-1", path: path.join(cwd, "artifact-1.log") }),
-		settings: Settings.isolated(),
+		settings: Settings.isolated({ "edit.enforceSeenLines": true }),
 		enableLsp: false,
 	} as ToolSession;
 }
@@ -331,12 +331,11 @@ describe("read → edit seen-line guard", () => {
 		expect(await Bun.file(file).text()).toBe(`${lines.join("\n")}\n`);
 	});
 
-	it("does not mark column-clipped read lines as seen", async () => {
+	it("marks column-clipped read lines as seen (clipped-line check removed)", async () => {
 		// A 4KB single line — the read tool's column cap (default 512 chars)
-		// clips this into `<prefix>…` in the numbered output. The clipped line
-		// number MUST stay out of the tag's seenLines, or a subsequent edit
-		// anchored there would slip past the seen-line guard having seen only
-		// the first 512 chars.
+		// clips this into `<prefix>…` in the numbered output. The clipped-line
+		// exclusion was removed, so the displayed line counts as seen and a
+		// follow-up edit anchored there applies even with the guard enabled.
 		const file = path.join(tmpDir, "wide.txt");
 		const wide = "a".repeat(4096);
 		const content = `head\n${wide}\nfoot\n`;
@@ -347,14 +346,10 @@ describe("read → edit seen-line guard", () => {
 		const tag = tagFromOutput(resultText(read));
 
 		const seen = getFileSnapshotStore(session).byHash(canonicalSnapshotKey(file), tag)?.seenLines;
-		expect(seen?.has(2)).toBe(false);
+		expect(seen?.has(2)).toBe(true);
 
-		// A straight edit anchored at the clipped line 2 is still rejected —
-		// the seen-line guard fires because the model only saw the prefix.
-		await expect(
-			executeHashlineSingle(execOptions(`[wide.txt#${tag}]\nSWAP 2.=2:\n+REPLACED`, session)),
-		).rejects.toThrow(/never displayed \(it showed/);
-		expect(await Bun.file(file).text()).toBe(content);
+		await executeHashlineSingle(execOptions(`[wide.txt#${tag}]\nSWAP 2.=2:\n+REPLACED`, session));
+		expect(await Bun.file(file).text()).toBe("head\nREPLACED\nfoot\n");
 	});
 });
 
@@ -381,7 +376,11 @@ describe("search → edit seen-line guard", () => {
 			getArtifactsDir: () => path.join(cwd, "artifacts"),
 			allocateOutputArtifact: async () => ({ id: "artifact-1", path: path.join(cwd, "artifact-1.log") }),
 			// Zero context so the seen set is exactly the matched lines.
-			settings: Settings.isolated({ "grep.contextBefore": 0, "grep.contextAfter": 0 }),
+			settings: Settings.isolated({
+				"grep.contextBefore": 0,
+				"grep.contextAfter": 0,
+				"edit.enforceSeenLines": true,
+			}),
 			enableLsp: false,
 		} as ToolSession;
 	}
@@ -419,3 +418,31 @@ describe("search → edit seen-line guard", () => {
 		expect(await Bun.file(file).text()).toBe(`${lines.join("\n")}\n`);
 	});
 });
+
+describe("seen-line guard disabled by default", () => {
+	let tmpDir: string;
+
+	beforeAll(async () => {
+		await Settings.init({ inMemory: true });
+	});
+	beforeEach(async () => {
+		tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), "seen-line-off-"));
+	});
+	afterEach(async () => {
+		await removeWithRetries(tmpDir);
+	});
+
+	it("applies an edit on an unseen line when edit.enforceSeenLines is off (default)", async () => {
+		const file = path.join(tmpDir, "notes.txt");
+		await Bun.write(file, CONTENT);
+		// createSession enables the guard; a default session leaves it off.
+		const session = { ...createSession(tmpDir), settings: Settings.isolated() } as ToolSession;
+
+		const read = await new ReadTool(session).execute("r1", { path: `${file}:1-3` });
+		const tag = tagFromOutput(resultText(read));
+
+		// Line 12 was never displayed, but the guard is disabled, so it applies.
+		await executeHashlineSingle(execOptions(`[notes.txt#${tag}]\nSWAP 12.=12:\n+EDITED`, session));
+		expect(await Bun.file(file).text()).toContain("EDITED");
+	});
+});

packages/hashline/CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added `enforceSeenLines` option to `PatcherOptions` to control whether seen-line validation is enforced on anchored edits; defaults to `true` for safety
+
+### Changed
+
+- Seen-line guard now respects `enforceSeenLines` setting; when `false`, tags validate on content hash alone without requiring lines to have been seen during reading
+
 ## [16.5.0] - 2026-07-13
 
 ### Fixed

packages/hashline/src/patcher.ts

@@ -73,6 +73,12 @@ export interface PatcherOptions {
 	 * host did not wire a resolver). Plain line-range ops never need it.
 	 */
 	blockResolver?: BlockResolver;
+	/**
+	 * Enforce the seen-line guard: reject anchored edits on lines the read/search
+	 * that minted the tag never displayed. Defaults to `true`. When `false`, tags
+	 * validate on content hash alone and any anchor into the tagged content applies.
+	 */
+	enforceSeenLines?: boolean;
 }
 
 /** Per-section result returned by {@link Patcher.apply} / {@link Patcher.commit}. */
@@ -197,6 +203,7 @@ export class Patcher {
 	readonly snapshots: SnapshotStore;
 	readonly recovery: Recovery;
 	readonly blockResolver: BlockResolver | undefined;
+	readonly #enforceSeenLines: boolean;
 
 	constructor(options: PatcherOptions) {
 		if (!options.snapshots) {
@@ -206,6 +213,7 @@ export class Patcher {
 		this.snapshots = options.snapshots;
 		this.recovery = new Recovery(options.snapshots);
 		this.blockResolver = options.blockResolver;
+		this.#enforceSeenLines = options.enforceSeenLines ?? true;
 	}
 
 	/**
@@ -628,7 +636,9 @@ export class Patcher {
 			// The line numbers in `edits` index the exact content the tag names.
 			// Reject any anchor the read never displayed: editing lines the model
 			// has not seen is the off-by-memory mistake that mangles files.
-			if (expected !== undefined) this.#assertSeenLines(section, expected, matchedSnapshot);
+			if (expected !== undefined && this.#enforceSeenLines) {
+				this.#assertSeenLines(section, expected, matchedSnapshot);
+			}
 			const result = applyEdits(normalized, resolved);
 			return withResolveWarnings(blockResolutions.length > 0 ? { ...result, blockResolutions } : result);
 		}