Merge pull request #1952 from gustavosmendes/codex/fix-write-existing-file-guard-1871

fix: make write-existing-file-guard read-gated with overwrite bypass

src/hooks/write-existing-file-guard/hook.ts

@@ -1,50 +1,262 @@
 import type { Hooks, PluginInput } from "@opencode-ai/plugin"
 
-import { existsSync } from "fs"
+import { existsSync, realpathSync } from "fs"
-import { resolve, isAbsolute, join, normalize, sep } from "path"
+import { basename, dirname, isAbsolute, join, normalize, relative, resolve, sep } from "path"
 
 import { log } from "../../shared"
 
+type GuardArgs = {
+  filePath?: string
+  path?: string
+  file_path?: string
+  overwrite?: boolean | string
+}
+
+const MAX_TRACKED_SESSIONS = 256
+export const MAX_TRACKED_PATHS_PER_SESSION = 1024
+const OUTSIDE_SESSION_MESSAGE = "Path must be inside session directory."
+
+function asRecord(value: unknown): Record<string, unknown> | undefined {
+  if (!value || typeof value !== "object" || Array.isArray(value)) {
+    return undefined
+  }
+
+  return value as Record<string, unknown>
+}
+
+function getPathFromArgs(args: GuardArgs | undefined): string | undefined {
+  return args?.filePath ?? args?.path ?? args?.file_path
+}
+
+function resolveInputPath(ctx: PluginInput, inputPath: string): string {
+  return normalize(isAbsolute(inputPath) ? inputPath : resolve(ctx.directory, inputPath))
+}
+
+function isPathInsideDirectory(pathToCheck: string, directory: string): boolean {
+  const relativePath = relative(directory, pathToCheck)
+  return relativePath === "" || (!relativePath.startsWith("..") && !isAbsolute(relativePath))
+}
+
+function toCanonicalPath(absolutePath: string): string {
+  let canonicalPath = absolutePath
+
+  if (existsSync(absolutePath)) {
+    try {
+      canonicalPath = realpathSync.native(absolutePath)
+    } catch {
+      canonicalPath = absolutePath
+    }
+  } else {
+    const absoluteDir = dirname(absolutePath)
+    const resolvedDir = existsSync(absoluteDir) ? realpathSync.native(absoluteDir) : absoluteDir
+    canonicalPath = join(resolvedDir, basename(absolutePath))
+  }
+
+  // Preserve canonical casing from the filesystem to avoid collapsing distinct
+  // files on case-sensitive volumes (supported on all major OSes).
+  return normalize(canonicalPath)
+}
+
+function isOverwriteEnabled(value: boolean | string | undefined): boolean {
+  if (value === true) {
+    return true
+  }
+
+  if (typeof value === "string") {
+    return value.toLowerCase() === "true"
+  }
+
+  return false
+}
+
 export function createWriteExistingFileGuardHook(ctx: PluginInput): Hooks {
-  return {
+  const readPermissionsBySession = new Map<string, Set<string>>()
-    "tool.execute.before": async (input, output) => {
+  const sessionLastAccess = new Map<string, number>()
-      const toolName = input.tool?.toLowerCase()
+  const canonicalSessionRoot = toCanonicalPath(resolveInputPath(ctx, ctx.directory))
-      if (toolName !== "write") {
+  const sisyphusRoot = join(canonicalSessionRoot, ".sisyphus") + sep
+
+  const touchSession = (sessionID: string): void => {
+    sessionLastAccess.set(sessionID, Date.now())
+  }
+
+  const evictLeastRecentlyUsedSession = (): void => {
+    let oldestSessionID: string | undefined
+    let oldestSeen = Number.POSITIVE_INFINITY
+
+    for (const [sessionID, lastSeen] of sessionLastAccess.entries()) {
+      if (lastSeen < oldestSeen) {
+        oldestSeen = lastSeen
+        oldestSessionID = sessionID
+      }
+    }
+
+    if (!oldestSessionID) {
+      return
+    }
+
+    readPermissionsBySession.delete(oldestSessionID)
+    sessionLastAccess.delete(oldestSessionID)
+  }
+
+  const ensureSessionReadSet = (sessionID: string): Set<string> => {
+    let readSet = readPermissionsBySession.get(sessionID)
+    if (!readSet) {
+      if (readPermissionsBySession.size >= MAX_TRACKED_SESSIONS) {
+        evictLeastRecentlyUsedSession()
+      }
+
+      readSet = new Set<string>()
+      readPermissionsBySession.set(sessionID, readSet)
+    }
+
+    touchSession(sessionID)
+    return readSet
+  }
+
+  const trimSessionReadSet = (readSet: Set<string>): void => {
+    while (readSet.size > MAX_TRACKED_PATHS_PER_SESSION) {
+      const oldestPath = readSet.values().next().value
+      if (!oldestPath) {
         return
       }
 
-      const args = output.args as
+      readSet.delete(oldestPath)
-        | { filePath?: string; path?: string; file_path?: string }
+    }
-        | undefined
+  }
-      const filePath = args?.filePath ?? args?.path ?? args?.file_path
+
+  const registerReadPermission = (sessionID: string, canonicalPath: string): void => {
+    const readSet = ensureSessionReadSet(sessionID)
+    if (readSet.has(canonicalPath)) {
+      readSet.delete(canonicalPath)
+    }
+
+    readSet.add(canonicalPath)
+    trimSessionReadSet(readSet)
+  }
+
+  const consumeReadPermission = (sessionID: string, canonicalPath: string): boolean => {
+    const readSet = readPermissionsBySession.get(sessionID)
+    if (!readSet || !readSet.has(canonicalPath)) {
+      return false
+    }
+
+    readSet.delete(canonicalPath)
+    touchSession(sessionID)
+    return true
+  }
+
+  const invalidateOtherSessions = (canonicalPath: string, writingSessionID?: string): void => {
+    for (const [sessionID, readSet] of readPermissionsBySession.entries()) {
+      if (writingSessionID && sessionID === writingSessionID) {
+        continue
+      }
+
+      readSet.delete(canonicalPath)
+    }
+  }
+
+  return {
+    "tool.execute.before": async (input, output) => {
+      const toolName = input.tool?.toLowerCase()
+      if (toolName !== "write" && toolName !== "read") {
+        return
+      }
+
+      const argsRecord = asRecord(output.args)
+      const args = argsRecord as GuardArgs | undefined
+      const filePath = getPathFromArgs(args)
       if (!filePath) {
         return
       }
 
-      const resolvedPath = normalize(
+      const resolvedPath = resolveInputPath(ctx, filePath)
-        isAbsolute(filePath) ? filePath : resolve(ctx.directory, filePath)
+      const canonicalPath = toCanonicalPath(resolvedPath)
-      )
+      const isInsideSessionDirectory = isPathInsideDirectory(canonicalPath, canonicalSessionRoot)
 
-      if (existsSync(resolvedPath)) {
+      if (!isInsideSessionDirectory) {
-        const sisyphusRoot = join(ctx.directory, ".sisyphus") + sep
+        if (toolName === "read") {
-        const isSisyphusMarkdown =
-          resolvedPath.startsWith(sisyphusRoot) && resolvedPath.endsWith(".md")
-        if (isSisyphusMarkdown) {
-          log("[write-existing-file-guard] Allowing .sisyphus/*.md overwrite", {
-            sessionID: input.sessionID,
-            filePath,
-          })
           return
         }
 
-        log("[write-existing-file-guard] Blocking write to existing file", {
+        log("[write-existing-file-guard] Blocking write outside session directory", {
           sessionID: input.sessionID,
           filePath,
           resolvedPath,
         })
-
+        throw new Error(OUTSIDE_SESSION_MESSAGE)
-        throw new Error("File already exists. Use edit tool instead.")
       }
+
+      if (toolName === "read") {
+        if (!existsSync(resolvedPath) || !input.sessionID) {
+          return
+        }
+
+        registerReadPermission(input.sessionID, canonicalPath)
+        return
+      }
+
+      const overwriteEnabled = isOverwriteEnabled(args?.overwrite)
+
+      if (argsRecord && "overwrite" in argsRecord) {
+        // Intentionally mutate output args so overwrite bypass remains hook-only.
+        delete argsRecord.overwrite
+      }
+
+      if (!existsSync(resolvedPath)) {
+        return
+      }
+
+      const isSisyphusPath = canonicalPath.startsWith(sisyphusRoot)
+      if (isSisyphusPath) {
+        log("[write-existing-file-guard] Allowing .sisyphus/** overwrite", {
+          sessionID: input.sessionID,
+          filePath,
+        })
+        invalidateOtherSessions(canonicalPath, input.sessionID)
+        return
+      }
+
+      if (overwriteEnabled) {
+        log("[write-existing-file-guard] Allowing overwrite flag bypass", {
+          sessionID: input.sessionID,
+          filePath,
+          resolvedPath,
+        })
+        invalidateOtherSessions(canonicalPath, input.sessionID)
+        return
+      }
+
+      if (input.sessionID && consumeReadPermission(input.sessionID, canonicalPath)) {
+        log("[write-existing-file-guard] Allowing overwrite after read", {
+          sessionID: input.sessionID,
+          filePath,
+          resolvedPath,
+        })
+        invalidateOtherSessions(canonicalPath, input.sessionID)
+        return
+      }
+
+      log("[write-existing-file-guard] Blocking write to existing file", {
+        sessionID: input.sessionID,
+        filePath,
+        resolvedPath,
+      })
+
+      throw new Error("File already exists. Use edit tool instead.")
+    },
+    event: async ({ event }: { event: { type: string; properties?: unknown } }) => {
+      if (event.type !== "session.deleted") {
+        return
+      }
+
+      const props = event.properties as { info?: { id?: string } } | undefined
+      const sessionID = props?.info?.id
+      if (!sessionID) {
+        return
+      }
+
+      readPermissionsBySession.delete(sessionID)
+      sessionLastAccess.delete(sessionID)
     },
   }
 }

src/hooks/write-existing-file-guard/index.test.ts

@@ -1,305 +1,551 @@
-import { describe, test, expect, beforeEach, afterEach } from "bun:test"
+import { afterEach, beforeEach, describe, expect, test } from "bun:test"
+import { existsSync, mkdirSync, mkdtempSync, rmSync, symlinkSync, writeFileSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { dirname, join, resolve } from "node:path"
+
+import { MAX_TRACKED_PATHS_PER_SESSION } from "./hook"
 import { createWriteExistingFileGuardHook } from "./index"
-import * as fs from "fs"
+
-import * as path from "path"
+const BLOCK_MESSAGE = "File already exists. Use edit tool instead."
-import * as os from "os"
+const OUTSIDE_SESSION_MESSAGE = "Path must be inside session directory."
+
+type Hook = ReturnType<typeof createWriteExistingFileGuardHook>
+
+function isCaseInsensitiveFilesystem(directory: string): boolean {
+  const probeName = `CaseProbe_${Date.now()}_A.txt`
+  const upperPath = join(directory, probeName)
+  const lowerPath = join(directory, probeName.toLowerCase())
+
+  writeFileSync(upperPath, "probe")
+  try {
+    return existsSync(lowerPath)
+  } finally {
+    rmSync(upperPath, { force: true })
+  }
+}
 
 describe("createWriteExistingFileGuardHook", () => {
-  let tempDir: string
+  let tempDir = ""
-  let ctx: { directory: string }
+  let hook: Hook
-  let hook: ReturnType<typeof createWriteExistingFileGuardHook>
+  let callCounter = 0
+
+  const createFile = (relativePath: string, content = "existing content"): string => {
+    const absolutePath = join(tempDir, relativePath)
+    mkdirSync(dirname(absolutePath), { recursive: true })
+    writeFileSync(absolutePath, content)
+    return absolutePath
+  }
+
+  const invoke = async (args: {
+    tool: string
+    sessionID?: string
+    outputArgs: Record<string, unknown>
+  }): Promise<{ args: Record<string, unknown> }> => {
+    callCounter += 1
+    const output = { args: args.outputArgs }
+
+    await hook["tool.execute.before"]?.(
+      {
+        tool: args.tool,
+        sessionID: args.sessionID ?? "ses_default",
+        callID: `call_${callCounter}`,
+      } as never,
+      output as never
+    )
+
+    return output
+  }
+
+  const emitSessionDeleted = async (sessionID: string): Promise<void> => {
+    await hook.event?.({ event: { type: "session.deleted", properties: { info: { id: sessionID } } } })
+  }
 
   beforeEach(() => {
-    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "write-guard-test-"))
+    tempDir = mkdtempSync(join(tmpdir(), "write-existing-file-guard-"))
-    ctx = { directory: tempDir }
+    hook = createWriteExistingFileGuardHook({ directory: tempDir } as never)
-    hook = createWriteExistingFileGuardHook(ctx as any)
+    callCounter = 0
   })
 
   afterEach(() => {
-    fs.rmSync(tempDir, { recursive: true, force: true })
+    rmSync(tempDir, { recursive: true, force: true })
   })
 
-  describe("tool.execute.before", () => {
+  test("#given non-existing file #when write executes #then allows", async () => {
-    test("allows write to non-existing file", async () => {
+    await expect(
-      //#given
+      invoke({
-      const nonExistingFile = path.join(tempDir, "new-file.txt")
+        tool: "write",
-      const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
+        outputArgs: { filePath: join(tempDir, "new-file.txt"), content: "new content" },
-      const output = { args: { filePath: nonExistingFile, content: "hello" } }
+      })
+    ).resolves.toBeDefined()
+  })
 
-      //#when
+  test("#given existing file without read or overwrite #when write executes #then blocks", async () => {
-      const result = hook["tool.execute.before"]?.(input as any, output as any)
+    const existingFile = createFile("existing.txt")
 
-      //#then
+    await expect(
-      await expect(result).resolves.toBeUndefined()
+      invoke({
+        tool: "write",
+        outputArgs: { filePath: existingFile, content: "new content" },
+      })
+    ).rejects.toThrow(BLOCK_MESSAGE)
+  })
+
+  test("#given same-session read #when write executes #then allows once and consumes permission", async () => {
+    const existingFile = createFile("consume-once.txt")
+    const sessionID = "ses_consume"
+
+    await invoke({
+      tool: "read",
+      sessionID,
+      outputArgs: { filePath: existingFile },
     })
 
-    test("blocks write to existing file", async () => {
+    await expect(
-      //#given
+      invoke({
-      const existingFile = path.join(tempDir, "existing-file.txt")
+        tool: "write",
-      fs.writeFileSync(existingFile, "existing content")
+        sessionID,
-      const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
+        outputArgs: { filePath: existingFile, content: "first overwrite" },
-      const output = { args: { filePath: existingFile, content: "new content" } }
+      })
+    ).resolves.toBeDefined()
 
-      //#when
+    await expect(
-      const result = hook["tool.execute.before"]?.(input as any, output as any)
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: existingFile, content: "second overwrite" },
+      })
+    ).rejects.toThrow(BLOCK_MESSAGE)
+  })
 
-      //#then
+  test("#given same-session concurrent writes #when only one read permission exists #then allows only one write", async () => {
-      await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
+    const existingFile = createFile("concurrent-consume.txt")
+    const sessionID = "ses_concurrent"
+
+    await invoke({
+      tool: "read",
+      sessionID,
+      outputArgs: { filePath: existingFile },
     })
 
-    test("blocks write tool (lowercase) to existing file", async () => {
+    const results = await Promise.allSettled([
-      //#given
+      invoke({
-      const existingFile = path.join(tempDir, "existing-file.txt")
+        tool: "write",
-      fs.writeFileSync(existingFile, "existing content")
+        sessionID,
-      const input = { tool: "write", sessionID: "ses_1", callID: "call_1" }
+        outputArgs: { filePath: existingFile, content: "first attempt" },
-      const output = { args: { filePath: existingFile, content: "new content" } }
+      }),
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: existingFile, content: "second attempt" },
+      }),
+    ])
 
-      //#when
+    const successCount = results.filter((result) => result.status === "fulfilled").length
-      const result = hook["tool.execute.before"]?.(input as any, output as any)
+    const failures = results.filter(
+      (result): result is PromiseRejectedResult => result.status === "rejected"
+    )
 
-      //#then
+    expect(successCount).toBe(1)
-      await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
+    expect(failures).toHaveLength(1)
+    expect(String(failures[0]?.reason)).toContain(BLOCK_MESSAGE)
+  })
+
+  test("#given read in another session #when write executes #then blocks", async () => {
+    const existingFile = createFile("cross-session.txt")
+
+    await invoke({
+      tool: "read",
+      sessionID: "ses_reader",
+      outputArgs: { filePath: existingFile },
     })
 
-    test("ignores non-write tools", async () => {
+    await expect(
-      //#given
+      invoke({
-      const existingFile = path.join(tempDir, "existing-file.txt")
+        tool: "write",
-      fs.writeFileSync(existingFile, "existing content")
+        sessionID: "ses_writer",
-      const input = { tool: "Edit", sessionID: "ses_1", callID: "call_1" }
+        outputArgs: { filePath: existingFile, content: "new content" },
-      const output = { args: { filePath: existingFile, content: "new content" } }
+      })
+    ).rejects.toThrow(BLOCK_MESSAGE)
+  })
 
-      //#when
+  test("#given overwrite true boolean #when write executes #then bypasses guard and strips overwrite", async () => {
-      const result = hook["tool.execute.before"]?.(input as any, output as any)
+    const existingFile = createFile("overwrite-boolean.txt")
 
-      //#then
+    const output = await invoke({
-      await expect(result).resolves.toBeUndefined()
+      tool: "write",
+      outputArgs: {
+        filePath: existingFile,
+        content: "new content",
+        overwrite: true,
+      },
     })
 
-    test("ignores tools without any file path arg", async () => {
+    expect(output.args.overwrite).toBeUndefined()
-      //#given
+  })
-      const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-      const output = { args: { command: "ls" } }
 
-      //#when
+  test("#given overwrite true string #when write executes #then bypasses guard and strips overwrite", async () => {
-      const result = hook["tool.execute.before"]?.(input as any, output as any)
+    const existingFile = createFile("overwrite-string.txt")
 
-      //#then
+    const output = await invoke({
-      await expect(result).resolves.toBeUndefined()
+      tool: "write",
+      outputArgs: {
+        filePath: existingFile,
+        content: "new content",
+        overwrite: "true",
+      },
     })
 
-    describe("alternative arg names", () => {
+    expect(output.args.overwrite).toBeUndefined()
-      test("blocks write using 'path' arg to existing file", async () => {
+  })
-        //#given
-        const existingFile = path.join(tempDir, "existing-file.txt")
-        fs.writeFileSync(existingFile, "existing content")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { path: existingFile, content: "new content" } }
 
-        //#when
+  test("#given overwrite falsy values #when write executes #then does not bypass guard", async () => {
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
+    const existingFile = createFile("overwrite-falsy.txt")
 
-        //#then
+    for (const overwrite of [false, "false"] as const) {
-        await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
+      await expect(
-      })
+        invoke({
+          tool: "write",
+          outputArgs: {
+            filePath: existingFile,
+            content: "new content",
+            overwrite,
+          },
+        })
+      ).rejects.toThrow(BLOCK_MESSAGE)
+    }
+  })
 
-      test("blocks write using 'file_path' arg to existing file", async () => {
+  test("#given two sessions read same file #when one writes #then other session is invalidated", async () => {
-        //#given
+    const existingFile = createFile("invalidate.txt")
-        const existingFile = path.join(tempDir, "existing-file.txt")
-        fs.writeFileSync(existingFile, "existing content")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { file_path: existingFile, content: "new content" } }
 
-        //#when
+    await invoke({
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
+      tool: "read",
-
+      sessionID: "ses_a",
-        //#then
+      outputArgs: { filePath: existingFile },
-        await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
+    })
-      })
+    await invoke({
-
+      tool: "read",
-      test("allows write using 'path' arg to non-existing file", async () => {
+      sessionID: "ses_b",
-        //#given
+      outputArgs: { filePath: existingFile },
-        const nonExistingFile = path.join(tempDir, "new-file.txt")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { path: nonExistingFile, content: "hello" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).resolves.toBeUndefined()
-      })
-
-      test("allows write using 'file_path' arg to non-existing file", async () => {
-        //#given
-        const nonExistingFile = path.join(tempDir, "new-file.txt")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { file_path: nonExistingFile, content: "hello" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).resolves.toBeUndefined()
-      })
     })
 
-    describe("relative path resolution using ctx.directory", () => {
+    await expect(
-      test("blocks write to existing file using relative path", async () => {
+      invoke({
-        //#given
+        tool: "write",
-        const existingFile = path.join(tempDir, "existing-file.txt")
+        sessionID: "ses_b",
-        fs.writeFileSync(existingFile, "existing content")
+        outputArgs: { filePath: existingFile, content: "updated by B" },
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
+      })
-        const output = { args: { filePath: "existing-file.txt", content: "new content" } }
+    ).resolves.toBeDefined()
 
-        //#when
+    await expect(
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
+      invoke({
+        tool: "write",
+        sessionID: "ses_a",
+        outputArgs: { filePath: existingFile, content: "updated by A" },
+      })
+    ).rejects.toThrow(BLOCK_MESSAGE)
+  })
 
-        //#then
+  test("#given existing file under .sisyphus #when write executes #then always allows", async () => {
-        await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
+    const existingFile = createFile(".sisyphus/plans/plan.txt")
+
+    await expect(
+      invoke({
+        tool: "write",
+        outputArgs: { filePath: existingFile, content: "new plan" },
+      })
+    ).resolves.toBeDefined()
+  })
+
+  test("#given file arg variants #when read then write executes #then supports all variants", async () => {
+    const existingFile = createFile("variants.txt")
+    const variants: Array<"filePath" | "path" | "file_path"> = [
+      "filePath",
+      "path",
+      "file_path",
+    ]
+
+    for (const variant of variants) {
+      const sessionID = `ses_${variant}`
+      await invoke({
+        tool: "read",
+        sessionID,
+        outputArgs: { [variant]: existingFile },
       })
 
-      test("allows write to non-existing file using relative path", async () => {
+      await expect(
-        //#given
+        invoke({
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
+          tool: "write",
-        const output = { args: { filePath: "new-file.txt", content: "hello" } }
+          sessionID,
+          outputArgs: { [variant]: existingFile, content: `overwrite via ${variant}` },
+        })
+      ).resolves.toBeDefined()
+    }
+  })
 
-        //#when
+  test("#given tools without file path arg #when write and read execute #then ignores safely", async () => {
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
+    await expect(
-
+      invoke({
-        //#then
+        tool: "write",
-        await expect(result).resolves.toBeUndefined()
+        outputArgs: { content: "no path" },
       })
+    ).resolves.toBeDefined()
 
-      test("blocks write to nested relative path when file exists", async () => {
+    await expect(
-        //#given
+      invoke({
-        const subDir = path.join(tempDir, "subdir")
+        tool: "read",
-        fs.mkdirSync(subDir)
+        outputArgs: {},
-        const existingFile = path.join(subDir, "existing.txt")
-        fs.writeFileSync(existingFile, "existing content")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { filePath: "subdir/existing.txt", content: "new content" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
       })
+    ).resolves.toBeDefined()
+  })
 
-      test("uses ctx.directory not process.cwd for relative path resolution", async () => {
+  test("#given non-read-write tool #when it executes #then does not grant write permission", async () => {
-        //#given
+    const existingFile = createFile("ignored-tool.txt")
-        const existingFile = path.join(tempDir, "test-file.txt")
+    const sessionID = "ses_ignored_tool"
-        fs.writeFileSync(existingFile, "content")
-        const differentCtx = { directory: tempDir }
-        const differentHook = createWriteExistingFileGuardHook(differentCtx as any)
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { filePath: "test-file.txt", content: "new" } }
 
-        //#when
+    await invoke({
-        const result = differentHook["tool.execute.before"]?.(input as any, output as any)
+      tool: "edit",
-
+      sessionID,
-       //#then
+      outputArgs: { filePath: existingFile, oldString: "old", newString: "new" },
-       await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
-     })
-
-    describe(".sisyphus/*.md exception", () => {
-      test("allows write to existing .sisyphus/plans/plan.md", async () => {
-        //#given
-        const sisyphusDir = path.join(tempDir, ".sisyphus", "plans")
-        fs.mkdirSync(sisyphusDir, { recursive: true })
-        const planFile = path.join(sisyphusDir, "plan.md")
-        fs.writeFileSync(planFile, "# Existing Plan")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { filePath: planFile, content: "# Updated Plan" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).resolves.toBeUndefined()
-      })
-
-      test("allows write to existing .sisyphus/notes.md", async () => {
-        //#given
-        const sisyphusDir = path.join(tempDir, ".sisyphus")
-        fs.mkdirSync(sisyphusDir, { recursive: true })
-        const notesFile = path.join(sisyphusDir, "notes.md")
-        fs.writeFileSync(notesFile, "# Notes")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { filePath: notesFile, content: "# Updated Notes" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).resolves.toBeUndefined()
-      })
-
-      test("allows write to existing .sisyphus/*.md using relative path", async () => {
-        //#given
-        const sisyphusDir = path.join(tempDir, ".sisyphus")
-        fs.mkdirSync(sisyphusDir, { recursive: true })
-        const planFile = path.join(sisyphusDir, "plan.md")
-        fs.writeFileSync(planFile, "# Plan")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { filePath: ".sisyphus/plan.md", content: "# Updated" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).resolves.toBeUndefined()
-      })
-
-      test("blocks write to existing .sisyphus/file.txt (non-markdown)", async () => {
-        //#given
-        const sisyphusDir = path.join(tempDir, ".sisyphus")
-        fs.mkdirSync(sisyphusDir, { recursive: true })
-        const textFile = path.join(sisyphusDir, "file.txt")
-        fs.writeFileSync(textFile, "content")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { filePath: textFile, content: "new content" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
-      })
-
-      test("blocks write when .sisyphus is in parent path but not under ctx.directory", async () => {
-        //#given
-        const fakeSisyphusParent = path.join(os.tmpdir(), ".sisyphus", "evil-project")
-        fs.mkdirSync(fakeSisyphusParent, { recursive: true })
-        const evilFile = path.join(fakeSisyphusParent, "plan.md")
-        fs.writeFileSync(evilFile, "# Evil Plan")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { filePath: evilFile, content: "# Hacked" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
-
-        // cleanup
-        fs.rmSync(path.join(os.tmpdir(), ".sisyphus"), { recursive: true, force: true })
-      })
-
-      test("blocks write to existing regular file (not in .sisyphus)", async () => {
-        //#given
-        const regularFile = path.join(tempDir, "regular.md")
-        fs.writeFileSync(regularFile, "# Regular")
-        const input = { tool: "Write", sessionID: "ses_1", callID: "call_1" }
-        const output = { args: { filePath: regularFile, content: "# Updated" } }
-
-        //#when
-        const result = hook["tool.execute.before"]?.(input as any, output as any)
-
-        //#then
-        await expect(result).rejects.toThrow("File already exists. Use edit tool instead.")
-      })
     })
-   })
+
-})
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: existingFile, content: "should block" },
+      })
+    ).rejects.toThrow(BLOCK_MESSAGE)
+  })
+
+  test("#given relative read and absolute write #when same session writes #then allows", async () => {
+    createFile("relative-absolute.txt")
+    const sessionID = "ses_relative_absolute"
+    const relativePath = "relative-absolute.txt"
+    const absolutePath = resolve(tempDir, relativePath)
+
+    await invoke({
+      tool: "read",
+      sessionID,
+      outputArgs: { filePath: relativePath },
+    })
+
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: absolutePath, content: "updated" },
+      })
+    ).resolves.toBeDefined()
+  })
+
+  test("#given existing file outside session directory #when write executes #then blocks", async () => {
+    const outsideDir = mkdtempSync(join(tmpdir(), "write-existing-file-guard-outside-"))
+
+    try {
+      const outsideFile = join(outsideDir, "outside.txt")
+      writeFileSync(outsideFile, "outside")
+
+      await expect(
+        invoke({
+          tool: "write",
+          outputArgs: { filePath: outsideFile, content: "attempted overwrite" },
+        })
+      ).rejects.toThrow(OUTSIDE_SESSION_MESSAGE)
+    } finally {
+      rmSync(outsideDir, { recursive: true, force: true })
+    }
+  })
+
+  test("#given session read permission #when session deleted #then permission is cleaned up", async () => {
+    const existingFile = createFile("session-cleanup.txt")
+    const sessionID = "ses_cleanup"
+
+    await invoke({
+      tool: "read",
+      sessionID,
+      outputArgs: { filePath: existingFile },
+    })
+
+    await emitSessionDeleted(sessionID)
+
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: existingFile, content: "after cleanup" },
+      })
+    ).rejects.toThrow(BLOCK_MESSAGE)
+  })
+
+  test("#given case-different read path #when writing canonical path #then follows platform behavior", async () => {
+    const canonicalFile = createFile("CaseFile.txt")
+    const lowerCasePath = join(tempDir, "casefile.txt")
+    const sessionID = "ses_case"
+    const isCaseInsensitiveFs = isCaseInsensitiveFilesystem(tempDir)
+
+    await invoke({
+      tool: "read",
+      sessionID,
+      outputArgs: { filePath: lowerCasePath },
+    })
+
+    const writeAttempt = invoke({
+      tool: "write",
+      sessionID,
+      outputArgs: { filePath: canonicalFile, content: "updated" },
+    })
+
+    if (isCaseInsensitiveFs) {
+      await expect(writeAttempt).resolves.toBeDefined()
+      return
+    }
+
+    await expect(writeAttempt).rejects.toThrow(BLOCK_MESSAGE)
+  })
+
+  test("#given read via symlink #when write via real path #then allows overwrite", async () => {
+    const targetFile = createFile("real/target.txt")
+    const symlinkPath = join(tempDir, "linked-target.txt")
+    const sessionID = "ses_symlink"
+
+    try {
+      symlinkSync(targetFile, symlinkPath)
+    } catch (error) {
+      console.warn(
+        "Skipping symlink test: symlinks are not supported or cannot be created in this environment.",
+        error
+      )
+      return
+    }
+
+    await invoke({
+      tool: "read",
+      sessionID,
+      outputArgs: { filePath: symlinkPath },
+    })
+
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: targetFile, content: "updated via symlink read" },
+      })
+    ).resolves.toBeDefined()
+  })
+
+  test("#given session reads beyond path cap #when writing oldest and newest #then only newest is authorized", async () => {
+    const sessionID = "ses_path_cap"
+    const oldestFile = createFile("path-cap/0.txt")
+    let newestFile = oldestFile
+
+    await invoke({
+      tool: "read",
+      sessionID,
+      outputArgs: { filePath: oldestFile },
+    })
+
+    for (let index = 1; index <= MAX_TRACKED_PATHS_PER_SESSION; index += 1) {
+      newestFile = createFile(`path-cap/${index}.txt`)
+      await invoke({
+        tool: "read",
+        sessionID,
+        outputArgs: { filePath: newestFile },
+      })
+    }
+
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: oldestFile, content: "stale write" },
+      })
+    ).rejects.toThrow(BLOCK_MESSAGE)
+
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: newestFile, content: "fresh write" },
+      })
+    ).resolves.toBeDefined()
+  })
+
+  test("#given recently active session #when lru evicts #then keeps recent session permission", async () => {
+    const existingFile = createFile("lru.txt")
+    const hotSession = "ses_hot"
+
+    await invoke({
+      tool: "read",
+      sessionID: hotSession,
+      outputArgs: { filePath: existingFile },
+    })
+
+    for (let index = 0; index < 255; index += 1) {
+      await invoke({
+        tool: "read",
+        sessionID: `ses_${index}`,
+        outputArgs: { filePath: existingFile },
+      })
+    }
+
+    await new Promise((resolvePromise) => setTimeout(resolvePromise, 2))
+
+    await invoke({
+      tool: "read",
+      sessionID: hotSession,
+      outputArgs: { filePath: existingFile },
+    })
+
+    await invoke({
+      tool: "read",
+      sessionID: "ses_overflow",
+      outputArgs: { filePath: existingFile },
+    })
+
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID: hotSession,
+        outputArgs: { filePath: existingFile, content: "hot session write" },
+      })
+    ).resolves.toBeDefined()
+  })
+
+  test("#given session permissions #when session deleted #then subsequent writes are blocked", async () => {
+    const existingFile = createFile("cleanup.txt")
+    const sessionID = "ses_cleanup"
+
+    // establish permission by reading the existing file
+    await invoke({
+      tool: "read",
+      sessionID,
+      outputArgs: { filePath: existingFile },
+    })
+
+    // sanity check: write should be allowed while the session is active
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: existingFile, content: "first write" },
+      })
+    ).resolves.toBeDefined()
+
+    // delete the session to trigger cleanup of any stored permissions/state
+    await invoke({
+      tool: "session.deleted",
+      sessionID,
+      outputArgs: {},
+    })
+
+    // after session deletion, the previous permissions must no longer apply
+    await expect(
+      invoke({
+        tool: "write",
+        sessionID,
+        outputArgs: { filePath: existingFile, content: "second write after delete" },
+      })
+    ).rejects.toThrow(BLOCK_MESSAGE)
+  })
 })

src/plugin/event.test.ts

@@ -383,3 +383,55 @@ type EventInput = { event: { type: string; properties?: Record<string, unknown>
 		expect(dispatchCalls[1].event.type).toBe("session.idle")
 	})
 })
+
+describe("createEventHandler - event forwarding", () => {
+	it("forwards session.deleted to write-existing-file-guard hook", async () => {
+		//#given
+		const forwardedEvents: EventInput[] = []
+		const disconnectedSessions: string[] = []
+		const deletedSessions: string[] = []
+		const eventHandler = createEventHandler({
+			ctx: {} as never,
+			pluginConfig: {} as never,
+			firstMessageVariantGate: {
+				markSessionCreated: () => {},
+				clear: () => {},
+			},
+			managers: {
+				skillMcpManager: {
+					disconnectSession: async (sessionID: string) => {
+						disconnectedSessions.push(sessionID)
+					},
+				},
+				tmuxSessionManager: {
+					onSessionCreated: async () => {},
+					onSessionDeleted: async ({ sessionID }: { sessionID: string }) => {
+						deletedSessions.push(sessionID)
+					},
+				},
+			} as never,
+			hooks: {
+				writeExistingFileGuard: {
+					event: async (input: EventInput) => {
+						forwardedEvents.push(input)
+					},
+				},
+			} as never,
+		})
+		const sessionID = "ses_forward_delete_event"
+
+		//#when
+		await eventHandler({
+			event: {
+				type: "session.deleted",
+				properties: { info: { id: sessionID } },
+			},
+		})
+
+		//#then
+		expect(forwardedEvents.length).toBe(1)
+		expect(forwardedEvents[0]?.event.type).toBe("session.deleted")
+		expect(disconnectedSessions).toEqual([sessionID])
+		expect(deletedSessions).toEqual([sessionID])
+	})
+})

src/plugin/event.ts

@@ -48,6 +48,7 @@ export function createEventHandler(args: {
     await Promise.resolve(hooks.ralphLoop?.event?.(input))
     await Promise.resolve(hooks.stopContinuationGuard?.event?.(input))
     await Promise.resolve(hooks.compactionTodoPreserver?.event?.(input))
+    await Promise.resolve(hooks.writeExistingFileGuard?.event?.(input))
     await Promise.resolve(hooks.atlasHook?.handler?.(input))
   }