Pullrun

v0.6.0 — Reference-Counted rmi with Cascade Subtree Deletion

Per-node refcounts enable immediate cascade deletion when the last tag
referencing a root is removed. Shared layers are preserved — a child
node is only deleted when every parent referencing it has been removed.

Features

• pullrun rmi — remove an image by tag or digest. Cascading BFS
  subtree deletion on last-tag removal. Shared layers preserved
  (cascade stops at refcount > 0).
• Reference-counted DAG store — per-node node.refcount sidecar
  files (u64 LE, crash-atomic via write-then-rename).
• Crash recovery — recompute_all_refcounts on daemon startup
  rebuilds refcounts from all tagged image and workload roots.
• ListImages — now returns actual tagged-image data with
  DAG-walked total blob sizes (was empty stub).
• Compute image size — compute_image_size() BFS-walks the
  DAG and sums all blob.raw file sizes.

Fixes

• recompute_all_refcounts — uses HashMap accumulator instead of
  incrementing on stale files. Completely overwrites prior state.
• remove_image — decrements refcount BEFORE removing tag entries
  (crash between the two no longer orphans data forever).
• put()/put_blocking() — warn on refcount increment failure
  instead of silently dropping the error.
• pullrun-init and pullrun-vsock — switched to
  version.workspace = true (were hardcoded).

Tests

• 8 new refcount tests covering roundtrip, shared-layer cascade,
  multi-tag roots, stale-state recompute, missing-node handling,
  directory cleanup, and image size computation.
• 175 total passing tests (was 159).

Breaking Changes

• None. The refcount system is additive and fully backward-compatible
  with existing stores. Nodes without refcount files read as 0.