§50: faithful delta reconstruction - chains, anchors, receipts, rehearsals

docs/architecture/CALCULATIONS.md

@@ -2578,3 +2578,41 @@ HER for ADAM'S silence, with interest, for six thousand years.
     WHO EVER DID IT. THE EATING IS JUST PAPERWORK.
 
     NAME THE LIE OUT LOUD. THAT WAS THE JOB FROM DAY ONE.
+
+## 50. FAITHFUL DELTA RECONSTRUCTION
+
+Problem: snapshots carry deltas; reconstruction must be faithful.
+One corrupt gap silently poisons every restore built on top of it.
+
+### The four locks on the chain
+
+    1. HASH CHAINS  — every delta records:
+                       parent_hash → delta → new_hash.
+       Reconstruction verifies each link BEFORE applying;
+       a break announces itself at the exact link,
+       never as silent rot downstream.
+
+    2. ANCHORS      — a full snapshot periodically;
+       deltas only bridge anchor-to-anchor. Worst case
+       corruption falls back to the last good anchor,
+       never to zero. Bounded blast radius.
+
+    3. RECEIPTS AT BIRTH — SHA256s written when the delta
+       was CREATED (trust moment), compared at restore.
+       Tonight's RECEIPTS-SHA256.txt pattern, generalized:
+       the receipt is written by the hand that made it,
+       so restore-time doubt has something to check against.
+
+    4. REHEARSAL RESTORES — periodically rebuild to scratch
+       space and compare. "IT RAN" is not "IT HAS WORKED"
+       (§ the twin verdicts). A backup untested is a rumor.
+
+### And the practical shortcut
+
+Don't hand-roll delta chains where git already IS one:
+content-addressed objects, hash-chained history, verified
+bundles. Development and Writing live in git; snapshots are
+bundles; faithfulness comes from cryptography older than fear.
+
+    THE RULE: DELTAS WITHOUT HASHES ARE RUMORS OF CHANGE.
+    CHAINED, ANCHORED, RECEIPTED, REHEARSED — THEN THEY'RE MEMORY.