Empty clipboard payloads versus absent formats — 2026-09-22

The string/handle audit found that format availability was inferred from clipboard_len > 0 and clipboard_rtf_len > 0. Successfully storing a NUL-only payload therefore returned success but disappeared from Count, IsAvailable, Enum, GetClipboardData and the OLE wrapper.

Two explicit presence flags now distinguish that payload from an absent format. Lengths remain byte counts excluding NUL; allocated capacity can survive EmptyClipboard without advertising data. All production length writers were audited: public text storage, explicit RTF storage, RTF synthesis, native Edit copy, the RichEdit snapshot bridge, object-only projection removal and clearing. Format queries/enumeration and OLE wrapping read presence; copy loops and size calculations still read length. Retiring a buffer before growth clears its presence so an allocation failure cannot advertise it. No memory region or host mirror changed.

The interpretation follows the documented NUL-terminated CF_TEXT/CF_OEMTEXT representation and format-availability contract. This is not a fresh native Win98 observation. Empty registered RTF payloads are stored as bytes; the clipboard does not certify that they parse as RTF.

The public-handle regression covers empty text/OEM retrieval and locking, enumeration, empty registered RTF, synthesis from present empty text, clearing despite retained capacity, and OLE QueryGetData/GetData returning the one-byte terminator. The enum fixture now seeds presence explicitly. Native EDIT coverage checks that nonempty WM_COPY still publishes a format.

A compiler-only negative control restoring the pre-change runtime sources fails at empty text is a present format; no shared files or build artifacts are changed by that control. An early positive test exposed a fixture omission: the synthetic open transaction had no open HWND, so real EmptyClipboard correctly removed ownership and a subsequent SetClipboardData failed. The fixture now supplies that HWND rather than bypassing the handler.

Verification passes: expanded clipboard public-handle/OLE test, format enumeration, native Unicode EDIT (including clipboard copy), RTF 36/36, and fragment/ESP/logical-AND/quiet-inventory/tier/whitespace gates. The quiet inventory remains 248 manual + 22 metadata. Test coverage of the RichEdit snapshot producer is indirect; no WordPad UI run was performed.

Limitations: exact CountClipboardFormats accounting for synthesized/OLE formats, insertion-order enumeration, encodings, delayed rendering, ownership transfer and stale-handle lifetime remain open. Native control empty-paste semantics have not been established; the existing no-op policy is preserved and tested as current behavior, not asserted as Windows conformance. No browser, full-release, performance or native OOM result is claimed.