A chunk whose LLM response is truncated (`finish_reason="length"`) and can't be
recovered by splitting, or that hits the adaptive-retry depth cap, returns a
partial node set. Today that set is checkpointed and written to the content-hash
semantic cache + manifest-stamped as complete, so the incomplete nodes are
served forever until the file content changes or `--force`.
Truncated give-up results are now tagged with an internal `_partial` marker.
`save_semantic_cache` stamps the affected file's entry `partial: True` (detected
from the marker or an explicit `partial_source_files` arg), and `load_cached`
treats a partial entry as a cache MISS, so the file re-dispatches and retries.
The file is also left unstamped in the manifest (like a failed chunk, #933) so
detect_incremental re-queues it on the next incremental run — not only on a full
/ `--force` / content-change run. A file sliced across chunks accumulates via a
partial-aware `merge_existing` peek (`load_cached(allow_partial=True)`) so a
truncated slice is never dropped or silently promoted to complete. Self-heals: a
later complete extraction overwrites the same key with a non-partial entry. The
marker is stripped after the final save so it never leaks into graph.json.
