feat(hook): add fact-checking PreToolUse hook for Write/Edit tools

.opencode/hooks/enforce-factcheck-before-edit.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+# enforce-factcheck-before-edit.sh
+# PreToolUse hook: warns when Write/Edit tools are invoked without evidence of prior research
+# Exit 0 = pass (advisory only), stderr message becomes hook context
+
+TOOL="$OPENCODE_TOOL_NAME"
+INPUT="$OPENCODE_TOOL_INPUT"
+
+# Only apply to write/edit tools
+case "$TOOL" in
+  write|edit) ;;
+  *) exit 0 ;;
+esac
+
+# Check if tool input contains evidence of prior file reading
+if printf '%s\n' "$INPUT" | grep -qiE '(based on reading|as shown in|from the file|grep result|read tool output|line [0-9]+)'; then
+  echo "FACT-CHECK: Evidence of prior research detected" >&2
+  exit 0
+fi
+
+echo "FACT-CHECK WARNING: File edit attempted without evidence of reading the target file first. Best practice: read the file before editing." >&2
+exit 0

.opencode/opencode.jsonc

@@ -122,4 +122,16 @@
     "github-triage": false,
     "github-pr-search": false,
   },
+  "hooks": {
+    "PreToolUse": [
+      {
+        "command": ".opencode/hooks/enforce-factcheck-before-edit.sh",
+        "matcher": "write",
+      },
+      {
+        "command": ".opencode/hooks/enforce-factcheck-before-edit.sh",
+        "matcher": "edit",
+      },
+    ],
+  },
 }

packages/opencode/test/hook/factcheck.test.ts

@@ -0,0 +1,94 @@
+import path from "node:path"
+import { describe, expect, test } from "bun:test"
+import { runHook, type HookEnv } from "../../src/hook"
+
+const SCRIPT_PATH = path.resolve(
+  import.meta.dir,
+  "../../../../.opencode/hooks/enforce-factcheck-before-edit.sh",
+)
+
+function makeEnv(toolName: string, toolInput: string): HookEnv {
+  return {
+    OPENCODE_HOOK_EVENT: "PreToolUse",
+    OPENCODE_TOOL_NAME: toolName,
+    OPENCODE_TOOL_INPUT: toolInput,
+    OPENCODE_PROJECT_DIR: "/tmp/test",
+    OPENCODE_SESSION_ID: "test-session",
+  }
+}
+
+describe("enforce-factcheck-before-edit", () => {
+  test("passes non-edit tools without message", async () => {
+    const result = await runHook({ command: SCRIPT_PATH }, makeEnv("bash", "{}"))
+    expect(result.action).toBe("pass")
+    expect(result.message).toBeUndefined()
+  })
+
+  test("passes non-edit tool 'read'", async () => {
+    const result = await runHook({ command: SCRIPT_PATH }, makeEnv("read", '{"file":"/tmp/x"}'))
+    expect(result.action).toBe("pass")
+    expect(result.message).toBeUndefined()
+  })
+
+  test("warns on Write without evidence", async () => {
+    const result = await runHook(
+      { command: SCRIPT_PATH },
+      makeEnv("Write", '{"file_path":"/tmp/test.ts","content":"hello"}'),
+    )
+    expect(result.action).toBe("pass")
+    expect(result.message).toContain("FACT-CHECK WARNING")
+  })
+
+  test("warns on edit without evidence", async () => {
+    const result = await runHook(
+      { command: SCRIPT_PATH },
+      makeEnv("edit", '{"old_string":"foo","new_string":"bar"}'),
+    )
+    expect(result.action).toBe("pass")
+    expect(result.message).toContain("FACT-CHECK WARNING")
+  })
+
+  test("passes Edit with evidence phrase 'based on reading'", async () => {
+    const result = await runHook(
+      { command: SCRIPT_PATH },
+      makeEnv("Edit", '{"old_string":"based on reading the config"}'),
+    )
+    expect(result.action).toBe("pass")
+    expect(result.message).toContain("Evidence of prior research detected")
+  })
+
+  test("passes Write with evidence phrase 'line 42'", async () => {
+    const result = await runHook(
+      { command: SCRIPT_PATH },
+      makeEnv("Write", '{"content":"fix at line 42"}'),
+    )
+    expect(result.action).toBe("pass")
+    expect(result.message).toContain("Evidence of prior research detected")
+  })
+
+  test("passes write with evidence phrase 'grep result'", async () => {
+    const result = await runHook(
+      { command: SCRIPT_PATH },
+      makeEnv("write", '{"content":"grep result shows usage"}'),
+    )
+    expect(result.action).toBe("pass")
+    expect(result.message).toContain("Evidence of prior research detected")
+  })
+
+  test("passes Edit with evidence phrase 'read tool output'", async () => {
+    const result = await runHook(
+      { command: SCRIPT_PATH },
+      makeEnv("Edit", '{"old_string":"per read tool output"}'),
+    )
+    expect(result.action).toBe("pass")
+    expect(result.message).toContain("Evidence of prior research detected")
+  })
+
+  test("never blocks (advisory only)", async () => {
+    const result = await runHook(
+      { command: SCRIPT_PATH },
+      makeEnv("Write", '{"file_path":"/tmp/x","content":"no evidence here"}'),
+    )
+    expect(result.action).toBe("pass")
+  })
+})