fix(opencode): avoid rendering oversized snapshot diffs

packages/opencode/src/cli/cmd/run/scrollback.writer.tsx

@@ -7,6 +7,9 @@ import { toolFiletype, toolStructuredFinal } from "./tool"
 import { RUN_THEME_FALLBACK, transparent, type RunTheme } from "./theme"
 import type { EntryLayout, RunEntryBody, ScrollbackOptions, StreamCommit } from "./types"
 
+const MAX_DIFF_RENDER_CHARS = 512 * 1024
+const MAX_DIFF_RENDER_LINES = 5_000
+
 function todoText(item: { status: string; content: string }): string {
   if (item.status === "completed") {
     return `[✓] ${item.content}`
@@ -27,6 +30,17 @@ function todoColor(theme: RunTheme, status: string) {
   return status === "in_progress" ? theme.footer.warning : theme.block.muted
 }
 
+function tooLargeDiff(diff: string) {
+  if (diff.length > MAX_DIFF_RENDER_CHARS) return true
+  let lines = 1
+  for (let i = 0; i < diff.length; i++) {
+    if (diff.charCodeAt(i) !== 10) continue
+    lines++
+    if (lines > MAX_DIFF_RENDER_LINES) return true
+  }
+  return false
+}
+
 export function entryGroupKey(commit: StreamCommit): string | undefined {
   if (!commit.partID) {
     return undefined
@@ -193,27 +207,33 @@ export function RunEntryContent(props: {
                 {item.title}
               </text>
               {item.diff.trim() ? (
-                <box width="100%" paddingLeft={1}>
-                  <diff
-                    diff={item.diff}
-                    view="unified"
-                    filetype={toolFiletype(item.file)}
-                    syntaxStyle={syntax()}
-                    showLineNumbers={true}
-                    width="100%"
-                    wrapMode="word"
-                    fg={theme().block.text}
-                    addedBg={diffBg(theme().block.diffAddedBg)}
-                    removedBg={diffBg(theme().block.diffRemovedBg)}
-                    contextBg={diffBg(theme().block.diffContextBg)}
-                    addedSignColor={theme().block.diffHighlightAdded}
-                    removedSignColor={theme().block.diffHighlightRemoved}
-                    lineNumberFg={theme().block.diffLineNumber}
-                    lineNumberBg={diffBg(theme().block.diffContextBg)}
-                    addedLineNumberBg={diffBg(theme().block.diffAddedLineNumberBg)}
-                    removedLineNumberBg={diffBg(theme().block.diffRemovedLineNumberBg)}
-                  />
-                </box>
+                tooLargeDiff(item.diff) ? (
+                  <text width="100%" wrapMode="word" fg={theme().block.muted}>
+                    Diff too large to render safely; open the file or inspect the patch from disk.
+                  </text>
+                ) : (
+                  <box width="100%" paddingLeft={1}>
+                    <diff
+                      diff={item.diff}
+                      view="unified"
+                      filetype={toolFiletype(item.file)}
+                      syntaxStyle={syntax()}
+                      showLineNumbers={true}
+                      width="100%"
+                      wrapMode="word"
+                      fg={theme().block.text}
+                      addedBg={diffBg(theme().block.diffAddedBg)}
+                      removedBg={diffBg(theme().block.diffRemovedBg)}
+                      contextBg={diffBg(theme().block.diffContextBg)}
+                      addedSignColor={theme().block.diffHighlightAdded}
+                      removedSignColor={theme().block.diffHighlightRemoved}
+                      lineNumberFg={theme().block.diffLineNumber}
+                      lineNumberBg={diffBg(theme().block.diffContextBg)}
+                      addedLineNumberBg={diffBg(theme().block.diffAddedLineNumberBg)}
+                      removedLineNumberBg={diffBg(theme().block.diffRemovedLineNumberBg)}
+                    />
+                  </box>
+                )
               ) : (
                 <text width="100%" wrapMode="word" fg={theme().block.diffRemoved}>
                   -{item.deletions ?? 0} line{item.deletions === 1 ? "" : "s"}

packages/opencode/src/snapshot/index.ts

@@ -1,6 +1,5 @@
 import { Cause, Duration, Effect, Layer, Schedule, Schema, Semaphore, Context } from "effect"
 import { ChildProcess, ChildProcessSpawner } from "effect/unstable/process"
-import { formatPatch, structuredPatch } from "diff"
 import path from "path"
 import { AppProcess } from "@opencode-ai/core/process"
 import { InstanceState } from "@/effect/instance-state"
@@ -31,6 +30,9 @@ export type FileDiff = typeof FileDiff.Type
 const log = Log.create({ service: "snapshot" })
 const prune = "7.days"
 const limit = 2 * 1024 * 1024
+const diffPatchLineLimit = 1_000
+const diffPatchByteLimit = 256 * 1024
+const diffPatchTotalByteLimit = 2 * 1024 * 1024
 const core = ["-c", "core.longpaths=true", "-c", "core.symlinks=true"]
 const cfg = ["-c", "core.autocrlf=false", ...core]
 const quote = [...cfg, "-c", "core.quotepath=false"]
@@ -506,133 +508,6 @@ export const layer: Layer.Layer<Service, never, AppFileSystem.Service | AppProce
                   deletions: number
                 }
 
-                type Ref = {
-                  file: string
-                  side: "before" | "after"
-                  ref: string
-                }
-
-                const show = Effect.fnUntraced(function* (row: Row) {
-                  if (row.binary) return ["", ""]
-                  if (row.status === "added") {
-                    return [
-                      "",
-                      yield* git([...cfg, ...args(["show", `${to}:${row.file}`])]).pipe(
-                        Effect.map((item) => item.text),
-                      ),
-                    ]
-                  }
-                  if (row.status === "deleted") {
-                    return [
-                      yield* git([...cfg, ...args(["show", `${from}:${row.file}`])]).pipe(
-                        Effect.map((item) => item.text),
-                      ),
-                      "",
-                    ]
-                  }
-                  return yield* Effect.all(
-                    [
-                      git([...cfg, ...args(["show", `${from}:${row.file}`])]).pipe(Effect.map((item) => item.text)),
-                      git([...cfg, ...args(["show", `${to}:${row.file}`])]).pipe(Effect.map((item) => item.text)),
-                    ],
-                    { concurrency: 2 },
-                  )
-                })
-
-                const load = Effect.fnUntraced(
-                  function* (rows: Row[]) {
-                    const refs = rows.flatMap((row) => {
-                      if (row.binary) return []
-                      if (row.status === "added")
-                        return [{ file: row.file, side: "after", ref: `${to}:${row.file}` } satisfies Ref]
-                      if (row.status === "deleted") {
-                        return [{ file: row.file, side: "before", ref: `${from}:${row.file}` } satisfies Ref]
-                      }
-                      return [
-                        { file: row.file, side: "before", ref: `${from}:${row.file}` } satisfies Ref,
-                        { file: row.file, side: "after", ref: `${to}:${row.file}` } satisfies Ref,
-                      ]
-                    })
-                    if (!refs.length) return new Map<string, { before: string; after: string }>()
-
-                    const batch = yield* appProcess.run(
-                      ChildProcess.make("git", [...cfg, ...args(["cat-file", "--batch"])], {
-                        cwd: state.directory,
-                        extendEnv: true,
-                      }),
-                      { stdin: refs.map((item) => item.ref).join("\n") + "\n" },
-                    )
-                    if (batch.exitCode !== 0) {
-                      log.info("git cat-file --batch failed during snapshot diff, falling back to per-file git show", {
-                        stderr: batch.stderr.toString("utf8"),
-                        refs: refs.length,
-                      })
-                      return
-                    }
-                    const out = batch.stdout
-
-                    const fail = (msg: string, extra?: Record<string, string>) => {
-                      log.info(msg, { ...extra, refs: refs.length })
-                      return undefined
-                    }
-
-                    const map = new Map<string, { before: string; after: string }>()
-                    const dec = new TextDecoder()
-                    let i = 0
-                    for (const ref of refs) {
-                      let end = i
-                      while (end < out.length && out[end] !== 10) end += 1
-                      if (end >= out.length) {
-                        return fail(
-                          "git cat-file --batch returned a truncated header during snapshot diff, falling back to per-file git show",
-                        )
-                      }
-
-                      const head = dec.decode(out.slice(i, end))
-                      i = end + 1
-                      const hit = map.get(ref.file) ?? { before: "", after: "" }
-                      if (head.endsWith(" missing")) {
-                        map.set(ref.file, hit)
-                        continue
-                      }
-
-                      const match = head.match(/^[0-9a-f]+ blob (\d+)$/)
-                      if (!match) {
-                        return fail(
-                          "git cat-file --batch returned an unexpected header during snapshot diff, falling back to per-file git show",
-                          { head },
-                        )
-                      }
-
-                      const size = Number(match[1])
-                      if (!Number.isInteger(size) || size < 0 || i + size >= out.length || out[i + size] !== 10) {
-                        return fail(
-                          "git cat-file --batch returned truncated content during snapshot diff, falling back to per-file git show",
-                          { head },
-                        )
-                      }
-
-                      const text = dec.decode(out.slice(i, i + size))
-                      if (ref.side === "before") hit.before = text
-                      if (ref.side === "after") hit.after = text
-                      map.set(ref.file, hit)
-                      i += size + 1
-                    }
-
-                    if (i !== out.length) {
-                      return fail(
-                        "git cat-file --batch returned trailing data during snapshot diff, falling back to per-file git show",
-                      )
-                    }
-
-                    return map
-                  },
-                  Effect.scoped,
-                  Effect.catch(() =>
-                    Effect.succeed<Map<string, { before: string; after: string }> | undefined>(undefined),
-                  ),
-                )
-
                 const result: FileDiff[] = []
                 const status = new Map<string, "added" | "deleted" | "modified">()
 
@@ -684,25 +559,69 @@ export const layer: Layer.Layer<Service, never, AppFileSystem.Service | AppProce
                   rows.push(...filtered)
                 }
 
-                const step = 100
-                const patch = (file: string, before: string, after: string) =>
-                  formatPatch(structuredPatch(file, file, before, after, "", "", { context: Number.MAX_SAFE_INTEGER }))
+                let totalPatchBytes = 0
+                const patch = Effect.fnUntraced(function* (row: Row) {
+                  if (row.binary) return ""
+                  const changed = row.additions + row.deletions
+                  if (changed > diffPatchLineLimit) {
+                    log.info("snapshot diff patch skipped because changed line limit was exceeded", {
+                      file: row.file,
+                      changed,
+                      max: diffPatchLineLimit,
+                    })
+                    return
+                  }
+                  if (totalPatchBytes >= diffPatchTotalByteLimit) return
 
-                for (let i = 0; i < rows.length; i += step) {
-                  const run = rows.slice(i, i + step)
-                  const text = yield* load(run)
+                  const patch = yield* git(
+                    [
+                      ...quote,
+                      ...args(["diff", "--no-ext-diff", "--no-renames", "--unified=3", from, to, "--", row.file]),
+                    ],
+                    { cwd: state.directory },
+                  )
+                  if (patch.code !== 0) {
+                    log.warn("failed to get snapshot file patch", {
+                      file: row.file,
+                      exitCode: patch.code,
+                      stderr: patch.stderr,
+                    })
+                    return
+                  }
 
-                  for (const row of run) {
-                    const hit = text?.get(row.file) ?? { before: "", after: "" }
-                    const [before, after] = row.binary ? ["", ""] : text ? [hit.before, hit.after] : yield* show(row)
-                    result.push({
+                  const text = patch.text.trimEnd()
+                  if (!text) return ""
+                  const bytes = Buffer.byteLength(text)
+                  if (bytes > diffPatchByteLimit) {
+                    log.info("snapshot diff patch skipped because byte limit was exceeded", {
+                      file: row.file,
+                      bytes,
+                      max: diffPatchByteLimit,
+                    })
+                    return
+                  }
+                  if (totalPatchBytes + bytes > diffPatchTotalByteLimit) {
+                    log.info("snapshot diff patch skipped because total byte limit was exceeded", {
                       file: row.file,
-                      patch: row.binary ? "" : patch(row.file, before, after),
-                      additions: row.additions,
-                      deletions: row.deletions,
-                      status: row.status,
+                      bytes: totalPatchBytes + bytes,
+                      max: diffPatchTotalByteLimit,
                     })
+                    return
                   }
+
+                  totalPatchBytes += bytes
+                  return text
+                })
+
+                for (const row of rows) {
+                  const item = yield* patch(row)
+                  result.push({
+                    file: row.file,
+                    ...(item === undefined ? {} : { patch: item }),
+                    additions: row.additions,
+                    deletions: row.deletions,
+                    status: row.status,
+                  })
                 }
 
                 return result

packages/opencode/test/snapshot/snapshot.test.ts

@@ -884,6 +884,25 @@ it.instance(
   { git: true },
 )
 
+it.instance(
+  "diffFull omits patches that are too large to render safely",
+  withTrackedSnapshot(({ tmp, snapshot, before }) =>
+    Effect.gen(function* () {
+      const lines = Array.from({ length: 1_200 }, (_, i) => `line-${i}`).join("\n")
+      yield* write(`${tmp.path}/large.txt`, lines)
+      const after = yield* snapshot.track()
+      expect(after).toBeTruthy()
+      const diffs = yield* snapshot.diffFull(before, after!)
+      const diff = diffs.find((item) => item.file === "large.txt")
+      expect(diff).toBeDefined()
+      expect(diff!.additions).toBe(1_200)
+      expect(diff!.deletions).toBe(0)
+      expect(diff!.patch).toBeUndefined()
+    }),
+  ),
+  { git: true },
+)
+
 it.instance(
   "diffFull with file modifications",
   withTrackedSnapshot(({ tmp, snapshot, before }) =>

packages/ui/src/components/session-turn.tsx

@@ -459,8 +459,8 @@ export function SessionTurn(
                     >
                       <For each={visible()}>
                         {(diff) => {
-                          const view = normalize(diff)
                           const active = createMemo(() => expanded().includes(diff.file))
+                          const view = createMemo(() => normalize(diff))
                           const [shown, setShown] = createSignal(false)
 
                           createEffect(
@@ -508,7 +508,7 @@ export function SessionTurn(
                               <Accordion.Content>
                                 <Show when={shown()}>
                                   <div data-slot="session-turn-diff-view" data-scrollable>
-                                    <Dynamic component={fileComponent} mode="diff" fileDiff={view.fileDiff} />
+                                    <Dynamic component={fileComponent} mode="diff" fileDiff={view().fileDiff} />
                                   </div>
                                 </Show>
                               </Accordion.Content>