CP shared KV HiCache now treats non-page-aligned valid-tail nodes as page-owned when a later request extends beyond them. The prefix probe, match path, insert path, and prepared backup start now agree on flooring the reusable prefix to the previous physical page boundary, so prepared backup metadata cannot start mid-page or fail to attach at insertion.
Duplicate frees under CP HiCache now go through a page-safe free helper. Insert and unfinished duplicate ranges free only fully unprotected pages; no-insert completion still releases the right tail owned only by the finishing request.
Constraint: CP HiCache allocator frees whole physical pages even when called with token-granular locs.
Rejected: Partial-page sharing/refcounting | too complex for the current page-as-minimum-unit contract.
Rejected: Fix only prepare_write_backup_for_req | match_prefix and insert would still expose exact valid-tail hits and desynchronize prepared backup length.
Confidence: medium
Scope-risk: moderate
Directive: Do not expose non-page-aligned CP valid-tail hits to extending requests unless partial-page ownership is explicitly implemented end-to-end.
Tested: remote g0034 py_compile for touched files
Tested: remote g0034 test_cp_hicache_metadata.py 97 passed
Tested: remote g0034 test_cp_shared_kv_runtime.py 73 passed
Not-tested: test_cp_shared_kv_layout.py aborts during installed sgl_kernel architecture-specific op loading before assertions
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