Adding a native patch to an already patched Peekaboo checkout could fail because a later patch changed the context needed to recognize an earlier one. This blocked the image-read and application-launch builds in #135 and #136.

The build now compares the checkout against complete ordered patch prefixes in a private Git index, applies only the missing suffix, and verifies the full result. Unexpected tracked or untracked changes still refuse before mutation; the real dependency index remains untouched. New patches append to the stack, with the independent close patch ordered after clipboard text so existing builds remain valid prefixes.

Related to #8. Validation passed using the actual helper block against six real pinned Git checkouts: pristine, previous text prefix, full stack, the previously landed close-before-text order, tracked drift, and untracked source drift. All successful cases reached the same expected source tree; full/drift cases and every real index stayed unchanged. `bun types`, `bun run ci`, and `git diff --check` pass. This changes build preparation only; no new native input or app launch was needed.

### Built in Ace

Used Codex terminal and file tools to reproduce the build failure, implement and review the correction, and validate real dependency checkouts under Nate’s explicit temporary exception to Ace-only development for #8. Ace’s normal signed build path exposed this blocker while developing native computer-use capabilities. The ongoing dogfooding gap is tracked in #5 and #8.