fix: [AI-450] auto-re-read stale files in agent loop so model sees current content

When `edit` or `write` tools fail with "modified since it was last read", the
agent loop now auto-re-reads the file and includes its current content in the
error response. This gives the model the fresh file state so it can adjust its
next edit accordingly, preventing infinite retry loops.

This approach preserves the original safety check in `FileTime.assert()` (the
tool still throws on stale files) but recovers at the agent level by:
1. Detecting stale file errors via regex match on the error message
2. Re-reading the file and updating `FileTime` read timestamp
3. Appending fresh file content to the error so the model sees current state

Also handles "must read file before overwriting" errors the same way.

Closes #450

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: anandgupta42

packages/opencode/src/session/processor.ts

@@ -19,6 +19,10 @@ import type { SessionID, MessageID } from "./schema"
 // altimate_change start — import Telemetry for per-generation token tracking
 import { Telemetry } from "@/altimate/telemetry"
 // altimate_change end
+// altimate_change start — import FileTime and Filesystem for stale file recovery (#450)
+import { FileTime } from "@/file/time"
+import { Filesystem } from "@/util/filesystem"
+// altimate_change end
 
 export namespace SessionProcessor {
   const DOOM_LOOP_THRESHOLD = 3
@@ -211,12 +215,29 @@ export namespace SessionProcessor {
                 case "tool-error": {
                   const match = toolcalls[value.toolCallId]
                   if (match && match.state.status === "running") {
+                    // altimate_change start — auto-read stale files so model sees current content (#450)
+                    let errorStr = (value.error as any).toString()
+                    const staleFileMatch =
+                      errorStr.match(/File (.+) has been modified since it was last read/) ??
+                      errorStr.match(/You must read file (.+) before overwriting it/)
+                    if (staleFileMatch) {
+                      const staleFilePath = staleFileMatch[1].trim()
+                      try {
+                        const freshContent = await Filesystem.readText(staleFilePath)
+                        FileTime.read(input.sessionID, staleFilePath)
+                        errorStr += `\n\nThe file has been auto-re-read. Here is the current content:\n<file path="${staleFilePath}">\n${freshContent}\n</file>`
+                        log.info("stale file auto-re-read", { file: staleFilePath, sessionID: input.sessionID })
+                      } catch (readErr) {
+                        log.warn("failed to auto-re-read stale file", { file: staleFilePath, error: readErr })
+                      }
+                    }
+                    // altimate_change end
                     await Session.updatePart({
                       ...match,
                       state: {
                         status: "error",
                         input: value.input ?? match.state.input,
-                        error: (value.error as any).toString(),
+                        error: errorStr,
                         time: {
                           start: match.state.time.start,
                           end: Date.now(),