Two failures from resumed kernel sessions: A resumed build re-runs debian/rules build, but the kernels keep their wrapper-step stamps in debian/stamps and the flavour config rule there exports .config from the annotations with no config prerequisite: the resumed build silently kept the previous attempt's configuration and a config edit never reached the .deb. Dropping the stamp cache unconditionally would impose the kernel packaging's shape on every package, so it is data-driven instead: packages declare the caches under a resume_clear quirk, and resumed builds remove those tree-relative paths before the build. The inner kbuild keeps its own incremental state, so only the cheap wrapper passes re-run and config-affected objects recompile. A SIGKILLed build (OOM) leaves its overlay mounts and /proc bind mount behind, and overlayfs creates root-owned work state inside the workdir: the next plain build (recording is always on, it replaces the session of its identity) failed to clear the leftovers with a permission error. Session clearing now unmounts everything under each entry at depth (re-reading /proc/mounts, tolerating mount stacks from consecutive crashes) and escalates through sudo; when the tree still cannot be cleared, the build reports it and continues without a session instead of layering over a half-cleared one.