fix(core): report read length and cap limits and long lines (#51011)

packages/core/src/tool/plugin/read.ts

@@ -20,7 +20,7 @@ const LocationInput = Schema.Struct({
     description: "The line or directory entry to start reading from (1-based)",
   }),
   limit: ReadToolFileSystem.PageInput.fields.limit.annotate({
-    description: "The maximum number of lines or directory entries to read (defaults to 2000)",
+    description: "The maximum number of lines or directory entries to read (defaults to and capped at 2000)",
   }),
 })
 export const Input = LocationInput

packages/core/src/tool/read-filesystem.ts

@@ -42,10 +42,10 @@ export class MediaIngestLimitError extends Schema.TaggedError<MediaIngestLimitEr
 
 export class OffsetOutOfRangeError extends Schema.TaggedError<OffsetOutOfRangeError>()(
   "ReadTool.OffsetOutOfRangeError",
-  { offset: Schema.Number },
+  { offset: Schema.Number, lines: Schema.Number },
 ) {
   override get message() {
-    return `Offset ${this.offset} is out of range`
+    return `Offset ${this.offset} is out of range for this file (${this.lines} ${this.lines === 1 ? "line" : "lines"})`
   }
 }
 
@@ -68,7 +68,7 @@ export type ReadError =
 
 export const PageInput = Schema.Struct({
   offset: Schema.optionalKey(NonNegativeInt),
-  limit: Schema.optionalKey(NonNegativeInt.check(Schema.isLessThanOrEqualTo(MAX_READ_LINES))),
+  limit: Schema.optionalKey(NonNegativeInt),
 })
 export type PageInput = typeof PageInput.Type
 
@@ -155,7 +155,7 @@ export const read = Effect.fn("ReadTool.read")(function* (
       type: "file" as const,
       uri: pathToFileURL(input).href,
       name: path.basename(input),
-      content: new TextDecoder().decode(first.bytes),
+      content: new TextDecoder().decode(first.bytes).split("\n").map(clampLine).join("\n"),
       encoding: "utf8" as const,
       mime: mimeType(input),
     }
@@ -164,7 +164,13 @@ export const read = Effect.fn("ReadTool.read")(function* (
   if (first.bytes.length >= first.info.size) {
     const result = textPage(first.bytes, true, page)
     if (result === undefined) return yield* Effect.die("Read page did not settle for a complete first chunk")
-    return yield* makeTextPage(input, resource, result, first.bytes.subarray(0, result.consumed).includes(0))
+    return yield* makeTextPage(
+      input,
+      resource,
+      result,
+      first.bytes.subarray(0, result.consumed).includes(0),
+      lineCount(textLeaf(first.bytes).summary.lines, first.bytes.at(-1)),
+    )
   }
 
   const offset = page.offset || 1
@@ -201,7 +207,7 @@ export const read = Effect.fn("ReadTool.read")(function* (
           checked += leaf.summary.bytes
           return length > 0 && leaf.bytes.subarray(0, length).includes(0)
         })
-        return yield* makeTextPage(input, resource, translated, binary)
+        return yield* makeTextPage(input, resource, translated, binary, lineCount(lines, leaves.at(-1)?.bytes.at(-1)))
       }
     }
 
@@ -234,10 +240,11 @@ const makeTextPage = Effect.fnUntraced(function* (
   resource: string,
   result: NonNullable<ReturnType<typeof textPage>>,
   binary: boolean,
+  lines: number,
 ) {
   if (binary) return yield* new BinaryFileError({ resource })
   if (result.entries.length === 0 && result.offset !== 1)
-    return yield* new OffsetOutOfRangeError({ offset: result.offset })
+    return yield* new OffsetOutOfRangeError({ offset: result.offset, lines })
   return new TextPage({
     type: "text-page",
     content: result.entries.join("\n"),
@@ -298,7 +305,7 @@ const textPage = (bytes: Uint8Array, eof: boolean, page: PageInput) => {
       next = line
       break
     }
-    const text = value.length > MAX_LINE_LENGTH ? value.slice(0, MAX_LINE_LENGTH) + MAX_LINE_SUFFIX : value
+    const text = clampLine(value)
     const lineSize = Buffer.byteLength(text, "utf-8") + (entries.length > 0 ? 1 : 0)
     if (size + lineSize > MAX_READ_BYTES) {
       next = line
@@ -316,6 +323,12 @@ const textPage = (bytes: Uint8Array, eof: boolean, page: PageInput) => {
   return { entries, offset, next, consumed }
 }
 
+const clampLine = (line: string) =>
+  line.length > MAX_LINE_LENGTH ? line.slice(0, MAX_LINE_LENGTH) + MAX_LINE_SUFFIX : line
+
+// A trailing newline ends the last line instead of starting an empty one.
+const lineCount = (newlines: number, last: number | undefined) => newlines + (last === undefined || last === 10 ? 0 : 1)
+
 type TextSummary = { readonly bytes: number; readonly lines: number }
 // Request-local augmented rope. Subtree byte and newline weights locate a line
 // like an order-statistic query without repeatedly decoding the accumulated text.

packages/core/test/tool-read-filesystem.test.ts

@@ -223,7 +223,7 @@ describe("ReadToolFileSystem", () => {
       )
 
       expect(error).toBeInstanceOf(ReadToolFileSystem.OffsetOutOfRangeError)
-      expect(error.message).toBe("Offset 2 is out of range")
+      expect(error.message).toBe("Offset 2 is out of range for this file (1 line)")
     }),
   )
 

packages/core/test/tool-read.test.ts

@@ -577,7 +577,10 @@ describe("ReadTool", () => {
     Effect.gen(function* () {
       const registry = yield* Tool.Service
       for (const [error, message] of [
-        [new ReadToolFileSystem.OffsetOutOfRangeError({ offset: 10 }), "Offset 10 is out of range"],
+        [
+          new ReadToolFileSystem.OffsetOutOfRangeError({ offset: 10, lines: 3 }),
+          "Offset 10 is out of range for this file (3 lines)",
+        ],
         [
           new ReadToolFileSystem.PathKindError({ resource: "socket", expected: "a file" }),
           "Path is not a file: socket",