Downstream: zig-utils/zig-js#334\nDepends on downstream contract: zig-utils/zig-js#333\n\nAdd an opt-in, generic stop-the-world relocation mechanism without changing non-moving embedders.\n\n## Scope\n\n- Let a binding declare whether a marked cell kind is movable.\n- Reserve all same-size destinations before any old cell, root, edge, index, or publication metadata is mutated.\n- Roll back every unpublished destination on allocation failure with exact backing accounting.\n- Record old/new payloads, kind, size, and a stable logical ID for the complete plan.\n- Expose infallible strong/weak/atomic/interior resolver hooks to the binding for root and cell-edge rewriting.\n- Commit copied headers/payloads, indexes, owned-storage publication, and old-storage release in one world-stopped phase.\n- Preserve mark, age/generation, remembered-set, live-byte/cell, finalizer, and collection accounting.\n- Keep the default collector byte-for-byte non-moving when the binding omits relocation hooks.\n\n## Acceptance\n\n- [ ] Exact generic tests cover zero cells, mixed pinned/movable cells, all size classes, cycles, weak survivors/deaths, and stable identity.\n- [ ] Failure injection at every destination reservation proves the old graph, indexes, ownership, and accounting are unchanged.\n- [ ] Successful compaction releases evacuated storage without running live-cell finalizers.\n- [ ] Repeated normal, ReleaseSafe, and suppression-free TSan gates pass with zero leaks.\n- [ ] README/API documentation defines the binding contract and downstream zig-js consumes an exact commit.
Downstream: zig-utils/zig-js#334\nDepends on downstream contract: zig-utils/zig-js#333\n\nAdd an opt-in, generic stop-the-world relocation mechanism without changing non-moving embedders.\n\n## Scope\n\n- Let a binding declare whether a marked cell kind is movable.\n- Reserve all same-size destinations before any old cell, root, edge, index, or publication metadata is mutated.\n- Roll back every unpublished destination on allocation failure with exact backing accounting.\n- Record old/new payloads, kind, size, and a stable logical ID for the complete plan.\n- Expose infallible strong/weak/atomic/interior resolver hooks to the binding for root and cell-edge rewriting.\n- Commit copied headers/payloads, indexes, owned-storage publication, and old-storage release in one world-stopped phase.\n- Preserve mark, age/generation, remembered-set, live-byte/cell, finalizer, and collection accounting.\n- Keep the default collector byte-for-byte non-moving when the binding omits relocation hooks.\n\n## Acceptance\n\n- [ ] Exact generic tests cover zero cells, mixed pinned/movable cells, all size classes, cycles, weak survivors/deaths, and stable identity.\n- [ ] Failure injection at every destination reservation proves the old graph, indexes, ownership, and accounting are unchanged.\n- [ ] Successful compaction releases evacuated storage without running live-cell finalizers.\n- [ ] Repeated normal, ReleaseSafe, and suppression-free TSan gates pass with zero leaks.\n- [ ] README/API documentation defines the binding contract and downstream zig-js consumes an exact commit.