# Clipboard and QR presentation

`crates/storage` owns secret-presentation lifecycle and derived QR data. The
CLI receives an already selected `PresentationSecret` or generated password and
only writes storage-produced status or terminal-rendering bytes. It never
launches `xclip`, `wl-copy`, `pbcopy`, `qrencode`, an image viewer, or a shell.
The same byte-oriented APIs are ready for pass-otp code and URI results without
placing OTP parsing or calculation in a frontend.

## Clipboard lifecycle

The default clipboard lease is 45 seconds, matching upstream `pass`.
`clipboard_timeout_seconds` may configure 1 through 300 seconds. Before copying,
storage snapshots an existing UTF-8 clipboard value. At lease completion or
cancellation it reads the clipboard again:

- if the copied secret remains current, storage restores the previous text or
  clears a previous empty/non-text clipboard;
- if another application or the user supplied newer contents, storage leaves
  those contents untouched;
- if cleanup cannot be verified or completed, the operation returns a typed
  cleanup failure rather than claiming success.

The CLI deliberately remains alive during the lease. This lets X11 and Wayland
serve the selection and guarantees cleanup without spawning a daemon or helper.
Linux also marks copied text with the commonly supported password-manager hint
to discourage clipboard-history retention. macOS uses NSPasteboard, Windows
uses the native clipboard, and Linux uses direct X11 or Wayland data-control
protocols through the safe `arboard` adapter. Unsupported targets return a
typed unavailable result. Tests inject a byte-oriented backend and cover
expiry, restore, clear, cancellation, failure, and newer-content races without
touching the developer clipboard.

## QR data

`QrMatrix` encodes secret bytes with the pure-Rust `qrcode` implementation and
returns only dimensions and dark/light module queries. Its module buffer,
terminal rendering, and source payload all use zeroizing/redacted storage
objects. The terminal renderer supplies the standard four-module quiet zone,
square half-block cells, and no plaintext label or payload. Frontends can draw
the same matrix natively without regenerating or interpreting it.

Round-trip tests decode generated password, Unicode, and `otpauth://` matrices
with the test-only `rqrr` decoder. Empty and oversized payloads are typed errors,
and CLI tests prove `show` and `generate` clipboard/QR modes never emit their
plaintext values.
