fix(edit): add compact seen-line retries

packages/hashline/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added structured `UnseenLinesError.retryable` metadata so hosts can offer compact retry continuations only when every unseen anchor was revealed in full.
+
 ## [17.3.0] - 2026-08-13
 
 ### Fixed

packages/hashline/src/grammar.lark

@@ -1,6 +1,9 @@
-start: begin_patch file_patch+ end_patch
+start: retry_patch | begin_patch file_patch+ end_patch
 begin_patch: "*** Begin Patch" LF
 end_patch:   "*** End Patch" LF?
+retry_patch: "RETRY " UUID LF?
+UUID: /[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}/
+
 
 file_patch: file_header hunk+
 file_header: "[" filename "#" file_hash "]" LF

packages/hashline/src/patcher.ts

@@ -65,6 +65,20 @@ const SEEN_LINE_REVEAL_CAP = 40;
  */
 const SEEN_LINE_REVEAL_MAX_COLUMNS = 512;
 
+/**
+ * Seen-line rejection metadata for hosts that can offer an explicit retry
+ * continuation after presenting the revealed source to the caller.
+ */
+export class UnseenLinesError extends Error {
+	constructor(
+		message: string,
+		readonly retryable: boolean,
+	) {
+		super(message);
+		this.name = "UnseenLinesError";
+	}
+}
+
 export interface PatcherOptions {
 	/** Storage backend used for all reads and writes. */
 	fs: Filesystem;
@@ -650,7 +664,10 @@ export class Patcher {
 		if (!truncated) {
 			for (const { line } of revealed) seen.add(line);
 		}
-		throw new Error(unseenLinesMessage(section.path, unseen, expected, { lines: revealed, truncated }));
+		throw new UnseenLinesError(
+			unseenLinesMessage(section.path, unseen, expected, { lines: revealed, truncated }),
+			!truncated,
+		);
 	}
 	#mismatchError(
 		section: PatchSection,

packages/hashline/src/prompt.md

@@ -4,6 +4,10 @@ Line-anchored patch language: name original lines/gaps to replace, insert, cut,
 Section: `[PATH#TAG]`; `TAG`: 4-hex snapshot from latest `read`/`search`, REQUIRED each section. New files: `write`; hashline edits existing files only.
 </headers>
 
+<retry>
+Only after a seen-line rejection supplies a retry token: verify its revealed lines, then use exactly `RETRY TOKEN` to apply the stored unchanged patch without resending it. A retry is one-shot and revalidates live files. If intent changes, submit a revised full patch instead. NEVER invent or reuse tokens.
+</retry>
+
 <ops>
 `PUT N.=M:`: replace original inclusive lines N–M with body.
 `PUT N*:`: replace syntactic block beginning N; closing line resolved.

packages/hashline/test/patcher.test.ts

@@ -12,6 +12,7 @@ import {
 	NodeFilesystem,
 	Patch,
 	Patcher,
+	UnseenLinesError,
 	type WriteResult,
 } from "@oh-my-pi/hashline";
 
@@ -272,9 +273,13 @@ describe("Patcher seen-line provenance", () => {
 		const tag = snapshots.record(PATH, CONTENT, [1, 2]);
 		const patcher = new Patcher({ fs, snapshots });
 
-		await expect(patcher.apply(Patch.parse(`[${PATH}#${tag}]\nPUT 4-4:\n+L4`))).rejects.toThrow(
-			/never displayed \(it showed/,
-		);
+		const error = await patcher
+			.apply(Patch.parse(`[${PATH}#${tag}]\nPUT 4-4:\n+L4`))
+			.then(() => undefined)
+			.catch((cause: unknown) => cause);
+		expect(error).toBeInstanceOf(UnseenLinesError);
+		expect((error as UnseenLinesError).retryable).toBe(true);
+		expect((error as Error).message).toMatch(/never displayed \(it showed/);
 		expect(fs.get(PATH)).toBe(CONTENT);
 	});