Thanks for the PR! One suggestion: I'd vote to drop the timestamp entirely — both the date= field on @Generated and the existing wall-clock timestamps in the FFI banner and DoNotEditWarning banner.

Reasoning: embedding DateTime.UtcNow in generated source means p compile produces different bytes on every run, even when no input changed. That breaks content-hash-based caching (Bazel, container layer caches, etc.), inflates incremental rebuild scope, and makes diffs of regenerated output noisy without adding information a reader can actually use (the git commit and the compiler version tell you "when" more reliably). JSR-269 makes date optional precisely for this reason — @Generated(value = "P Compiler") on its own is the common shape and gives IDEs and lints everything they need.

If keeping the banners' human-readable "this is generated" message is desirable, the wording works fine without a timestamp: just "This file was auto-generated by the P compiler. Please do not edit manually."

Concretely this would simplify the diff a lot — the whole GenerationTimestampUtc / Inv plumbing in Constants.cs goes away, and the four WriteLine(Constants.GeneratedAnnotation) call sites just emit @Generated(value = "P Compiler").

Bonus: if you'd ever want a timestamp back later, the reproducible-builds convention is to honor a SOURCE_DATE_EPOCH env var when set, falling back to no timestamp otherwise — that's an easy opt-in for users who genuinely want it.

(Separately, the Copilot review comment about UTC vs local-time mismatch looks stale — the current diff uses UTC consistently for both the annotation and the banners. Worth dismissing.)