Lossless index — value and capacity unchanged
What would lose capacity
| move | effect |
|---|---|
| reduce D | C_addr and k* both move (k* ∝ D) |
| INT8 / PQ / shorter codes on packed HVs | Hamming distances warp → k* cliffs earlier |
| drop traces | value gone |
A random HV in {+1,-1}^D has ~D bits of entropy. You cannot store it
in o(D) bits and keep the same geometry.
What does not lose either
Traces are already a = bind(x, ctx), v = token_hv, with x/ctx
built from Encoder._atom / _role (sha256 → random_hv).
Store the recipe (atom keys + bind/bundle/sequence). Rebuild with the same Encoder law. Measured here:
LOSSLESS_OK D=4096 bits_identical=3/3
Bit-identical packed buffers ⇒ identical Hamming ⇒ identical LSH
buckets ⇒ C_addr and k unchanged*. The value HV is the same object
in {+1,-1}^D.
Disk: integer keys instead of 2 * ceil(D/8) bytes. D stays 20 000.
Fallback
If a buffer is not in the Encoder algebra, keep it packed. That preserves value. It does not shrink that trace.
Code
palimseste/lossless.py — LosslessCodec.materialize + assert_bit_identical.
The 10.4 GB memory.bin is still the packed ULTRA dump. New writes
can be recipes. Converting the old dump is a separate pass: invert
each packed a against encode_sequence of the training windows.
Until that pass, do not delete packed parts.