Incremental compile

A full dub of the wasm cell is honest and slow. Incremental compile exists so a flipped {#if} does not relink libwasm, and so a host-only edit does not touch wasm at all. It is a cache discipline, not a second compiler.

Reprint-skip compares dest bytes. If they would not change, the file is not written and the mtime stays. Vite and dub then have no reason to rebuild that input. Opposite-cell-skip means a dirty +page.server.d does not relink wasm. compile --only FILE is the watch path: one kit source, one reprint.

The default no-LTO wasm cell can go further. Content-hash IR nodes, cache the emitted D, invalidate the route / component / layout cone, then ldc2 -c dirty src-d into .svelte-d/o/ and relink those objects with the libwasm .a set from dub describe. LTO cells (ldc-1.36 full, ldc-1.42 thin) stay whole-program dub. A hash-skip compile, or a touched .svelte whose dest bytes did not change, does not relink wasm. wasmDirty looks at write.json and at src-d/ / dub.sdl, not at the fact that you saved a file.

contentHash includes schema, kind, payload, child hashes, printer pin, and cell pin (LDC version plus libwasm or vibe.0 pin). A runtime bump cannot silently reuse objects. The printer pin is a string in compile.d; bumping it is how you force a world rebuild after an IR change.