L10: harden REPL history file permissions to 0600 (#82)

- cmd/odek/repl_editor.go: chmod existing repl_history to 0600 and open
  new files with O_WRONLY|O_CREATE|O_TRUNC and mode 0600, replacing the
  previous os.Create default permissions.
- cmd/odek/repl_editor_test.go: regression tests for restricted creation
  and hardening of existing world-readable files.
- docs/SECURITY.md + AGENTS.md: document L10 mitigation.

Author: jkyberneees

AGENTS.md

@@ -151,6 +151,7 @@ Layered prompt-injection / approval-fatigue defenses. Full reference: [docs/SECU
 - **Session file size cap** (`internal/session/session.go`) — session files larger than 32 MiB are rejected by `Load()` to prevent OOM from tampered or corrupted transcripts.
 - **Session ID write-path validation** (`internal/session/session.go`) — `saveLocked` validates `sess.ID` with `ValidateSessionID` before computing the destination path, and `Load` checks that the embedded ID matches the filename it was loaded from. A planted session file with an attacker-controlled `"id"` field can no longer redirect `Append`/`Save` to write outside the session directory.
 - **Skill file size cap** (`internal/skills/loader.go`) — `SKILL.md` files larger than 1 MiB are skipped so a malicious project cannot OOM the process at startup or bloat the system prompt.
+- **REPL history file permissions** (`cmd/odek/repl_editor.go`) — `~/.odek/repl_history` is now created/hardened with `0600` permissions (and any existing world-readable file is `chmod`d on the next persist), preventing local users from reading pasted API keys, tokens, and URLs from the REPL history.
 - **Serve sandbox default-on** — `odek serve` enables `--sandbox` automatically unless `--no-sandbox` is passed.
 - **Sandbox volume confinement** (`internal/sandbox/sandbox.go`) — extra `--sandbox-volume` host paths must resolve to a location under the working directory, cannot contain `..` or symlink escapes, and cannot match sensitive prefixes such as `/etc`, `/proc`, `/sys`, `/dev`, `/root`, `/home`, `/var`, `/run`, or `/var/run/docker.sock`.
 - **Sandbox read-only enforcement** (`cmd/odek/sandbox_file.go` + `cmd/odek/file_tool.go` + `cmd/odek/perf_tools.go`) — when a sandbox container is active, `write_file`, `patch`, and `batch_patch` translate host paths to `/workspace/...` and copy data into the container with `docker cp`, so a read-only workspace mount (`--sandbox-readonly`) is enforced for the agent's own file tools.

cmd/odek/repl_editor.go

@@ -488,7 +488,9 @@ func (h *replHistory) persist() {
 	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
 		return
 	}
-	f, err := os.Create(path)
+	// Harden any existing history file created with looser permissions.
+	_ = os.Chmod(path, 0600)
+	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
 	if err != nil {
 		return
 	}

cmd/odek/repl_editor_test.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// TestReplHistory_Persist_CreatesRestricted verifies that the REPL history
+// file is created with 0600 permissions.
+func TestReplHistory_Persist_CreatesRestricted(t *testing.T) {
+	origHome := os.Getenv("HOME")
+	home := t.TempDir()
+	os.Setenv("HOME", home)
+	defer os.Setenv("HOME", origHome)
+
+	h := newReplHistory()
+	path := filepath.Join(home, ".odek", historyFilename)
+	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, []byte{}, 0644); err != nil {
+		t.Fatal(err)
+	}
+	h.Load(path)
+	h.Add("secret-api-key")
+
+	fi, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("stat history file: %v", err)
+	}
+	if fi.Mode().Perm() != 0600 {
+		t.Errorf("history file mode = %o, want 0600", fi.Mode().Perm())
+	}
+}
+
+// TestReplHistory_Persist_HardensExisting verifies that an existing
+// world-readable history file is chmod'd to 0600 on the next persist.
+func TestReplHistory_Persist_HardensExisting(t *testing.T) {
+	origHome := os.Getenv("HOME")
+	home := t.TempDir()
+	os.Setenv("HOME", home)
+	defer os.Setenv("HOME", origHome)
+
+	path := filepath.Join(home, ".odek", historyFilename)
+	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, []byte("old\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	h := newReplHistory()
+	h.Load(path)
+	h.Add("new-secret")
+
+	fi, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("stat history file: %v", err)
+	}
+	if fi.Mode().Perm() != 0600 {
+		t.Errorf("history file mode = %o, want 0600", fi.Mode().Perm())
+	}
+}

docs/SECURITY.md

@@ -661,6 +661,12 @@ Now:
 
 `saveLocked` now calls `ValidateSessionID` before computing the filesystem path, and `Load` checks that the ID inside the file matches the filename it was loaded from. Any mismatch aborts the operation instead of following the attacker-controlled embedded ID.
 
+### 39m. REPL history file permissions
+
+`cmd/odek/repl_editor.go` created `~/.odek/repl_history` with `os.Create`, which uses mode `0666` masked by the process umask. On systems with a permissive umask, the file could be world-readable, leaking pasted API keys, tokens, and URLs to other local users.
+
+`persist()` now hardens any existing file with `os.Chmod(path, 0600)` and opens the file with `os.O_WRONLY|os.O_CREATE|os.O_TRUNC` and mode `0600`, matching the permission model already applied to sessions, audit logs, and Telegram logs.
+
 ### 40. `/api/resources` result limit cap
 
 The `/api/resources?q=...&limit=N` autocomplete endpoint previously accepted any positive `limit` value. It is now capped to 100 results both in the HTTP handler and in `Registry.Search`. This prevents a prompt-injected or attacker-forged request from forcing an unbounded directory walk and returning a multi-megabyte JSON response.