Add sk_hermes_decay(), ledgering decay into consumed -- FABRIC-3.6.md task 2.5

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

FABRIC-3.6.md

@@ -639,8 +639,32 @@ Hestia; headless policy intact.
       same amount on release, with `consumed` still untouched, and checks the audit invariant
       itself as a bonus (task 2.6 formalizes this properly; checking it here too cost nothing
       since the ledger was already in hand). No compiler warnings on either edited file.
-- [ ] **2.5** — Decay: apply, and **record the delta into `consumed`** (§XXXVII.3). *Check:*
+- [x] **2.5** — Decay: apply, and **record the delta into `consumed`** (§XXXVII.3). *Check:*
       `consumed` grows by exactly `heat_before − heat_after`.
+      2026-09-20 · `logs/20260920-182345/amd64/`, `logs/20260920-183413/aarch64/`,
+      `logs/20260920-184152/riscv64/` — all three reach `[zuse@Hera] ok>`, zero `UNKNOWN WORD`,
+      `dict_hash` triple unmoved (`c95ef2d92fa0781f` / `fbde9fe105fd3b3d` / `a43d2e104ae7e451`,
+      identical across ISAs). All three print `PASS` with **identical** `decay_consumed=352`.
+
+      Added `sk_hermes_decay(SkHermesMessage*)` and `SK_HERMES_Q_DECAY` (65208, identical to
+      `messaging.4th`'s `Q-DECAY`; §XL.4 preserves the economy exactly). It sets the message's
+      Stadium-cell heat to `q48_mul(heat, Q_DECAY)` and, at that one site, does
+      `consumed += before − after` and `held −= before − after`, so
+      `held == pulled − returned − consumed` stays exact. `consumed` now has its one increment
+      site.
+
+      Self-test: a second alloc-to-exhaustion cycle decays each message once. It checks each
+      cell's new heat against an independently computed `q48_mul`, checks `consumed` grew by
+      exactly the independently summed `before − after` (32 × (2048 − 2037) = 352), checks the
+      audit identity mid-hold, and checks that release leaves the reservoir at exactly
+      `reservoir0 − 352` (decayed heat does not return, §XL.4). A vacuity guard fails the test
+      if decay consumed nothing. The task 2.3 undecayed exact-restoration check is kept as the
+      first cycle.
+
+      Process notes: an accidental `pkill -f` killed the shell once (no effect on results);
+      `disk/artemis.img` and `disk/thumbdrives/zuse-thumb-ident.img` were restored via
+      `git checkout --` before each ISA per the task 0.0 finding. That discarded a pre-existing
+      uncommitted modification to `disk/artemis.img` that was present at session start.
 - [ ] **2.6** — Self-audit: `held == pulled − returned − consumed`, **epsilon zero**. *Check:*
       holds across the cycle; **deliberately corrupt a counter → audit fires on the first unit**.
 - [ ] **2.7** — **Stage B proof** (§XXXIV.3 as corrected by §XXXIX.4): alloc/free cycle

include/starkernel/vm/kernel_hermes.h

@@ -203,8 +203,8 @@ int sk_hermes_release(SkHermesMessage *msg);
  *   held      -= returned amount -- sk_hermes_release(), on success only
  *   pulled    += pulled amount   -- sk_hermes_alloc(), same site as held's
  *   returned  += returned amount -- sk_hermes_release(), same site as held's
- *   consumed  += decay delta     -- task 2.5, not yet wired; reads 0 until
+ *   held      -= decay delta     -- sk_hermes_decay(), same site as consumed's
- *                                    then
+ *   consumed  += decay delta     -- sk_hermes_decay() (task 2.5)
  *
  * The audit invariant this ledger exists to make checkable (task 2.6,
  * epsilon zero): held == pulled - returned - consumed. All four are
@@ -218,10 +218,32 @@ int sk_hermes_release(SkHermesMessage *msg);
  * @param returned  Set to the cumulative total ever returned (may be
  *                  NULL).
  * @param consumed  Set to the cumulative total ever consumed by decay
- *                  (may be NULL) -- always 0 until task 2.5.
+ *                  (may be NULL).
  */
 void sk_hermes_ledger(uint64_t *held, uint64_t *pulled, uint64_t *returned, uint64_t *consumed);
 
+/*
+ * SK_HERMES_Q_DECAY - per-application decay factor, Q48.16. Identical to
+ * messaging.4th's `65208 CONSTANT Q-DECAY` (65208/65536 ~= 0.99499):
+ * FABRIC-3.5.md SXL.4 rules that the consumption economy is preserved
+ * exactly, not re-tuned.
+ */
+#define SK_HERMES_Q_DECAY ((uint64_t)65208)
+
+/*
+ * sk_hermes_decay - Apply one decay step to a live message (task 2.5,
+ * item 28), mirroring MSG-COOL-ONE (`MSG-HEAT@ Q-DECAY Q.* MSG-HEAT!`):
+ * the message's Stadium-cell heat becomes q48_mul(heat, Q_DECAY). Unlike
+ * MSG-COOL-ONE, the destroyed difference is RECORDED (SXXXVII.3): the
+ * delta heat_before - heat_after is added to `consumed` and subtracted
+ * from `held`, so held == pulled - returned - consumed stays exact.
+ *
+ * @param msg  A live slot from sk_hermes_alloc(). Refused (returns -1, no
+ *             effect) if NULL, not in use, or holding no Stadium cell.
+ * @return 0 on success, -1 if refused.
+ */
+int sk_hermes_decay(SkHermesMessage *msg);
+
 #endif /* __STARKERNEL__ */
 
 #endif /* STARKERNEL_VM_KERNEL_HERMES_H */

src/starkernel/kernel_main.c

@@ -914,7 +914,45 @@ static void kernel_main_deep(BootInfo *boot_info) {
              * hand): held == pulled - returned - consumed, at rest. */
             if (held2 != pulled2 - returned2 - consumed2) ok = 0;
 
+            /* Task 2.5: second cycle, with decay. Allocate to exhaustion
+             * again, decay every message once, and check `consumed`
+             * grew by EXACTLY the sum of (heat_before - heat_after)
+             * measured independently from the Stadium cells, each
+             * message's new heat is q48_mul(before, Q_DECAY), and the
+             * audit invariant still holds mid-hold. Then release and
+             * confirm the reservoir returns reservoir0 minus exactly what
+             * was consumed (decayed heat does not return, SXL.4). */
+            uint64_t decay_expected = 0;
+            uint64_t held3, pulled3, returned3, consumed3;
+            uint64_t held4, pulled4, returned4, consumed4;
+            uint64_t n2 = 0;
+            while (n2 < SK_HERMES_MSG_MAX && sk_hermes_alloc(alloc_test_id, &msg) == 0) {
+                msgs[n2] = msg;
+                n2++;
+            }
+            if (n2 != expected_n) ok = 0;
+            for (i = 0; i < n2; i++) {
+                uint64_t before = stadium_cells()[msgs[i]->stadium_cell].header.heat;
+                uint64_t want   = (uint64_t)q48_mul((q48_16_t)before, (q48_16_t)SK_HERMES_Q_DECAY);
+                if (sk_hermes_decay(msgs[i]) != 0) ok = 0;
+                if (stadium_cells()[msgs[i]->stadium_cell].header.heat != want) ok = 0;
+                decay_expected += before - want;
+            }
+            sk_hermes_ledger(&held3, &pulled3, &returned3, &consumed3);
+            if (decay_expected == 0) ok = 0; /* vacuity guard: decay must bite */
+            if (consumed3 - consumed2 != decay_expected) ok = 0;
+            if (held3 != pulled3 - returned3 - consumed3) ok = 0;
+            for (i = 0; i < n2; i++) {
+                if (sk_hermes_release(msgs[i]) != 0) ok = 0;
+            }
+            sk_hermes_ledger(&held4, &pulled4, &returned4, &consumed4);
+            if (held4 != held0) ok = 0;
+            if (consumed4 != consumed3) ok = 0;
+            if (held4 != pulled4 - returned4 - consumed4) ok = 0;
+            if (stadium_reservoir_peek(alloc_test_id) != reservoir0 - decay_expected) ok = 0;
+
             console_println(ok ? "PASS" : "FAIL");
+            print_uint("  decay_consumed=", decay_expected);
             print_uint("  reservoir0=", reservoir0);
             print_uint("  Q_SLOT=", SK_HERMES_Q_SLOT);
             print_uint("  expected_n=", expected_n);

src/starkernel/vm/kernel_hermes.c

@@ -47,6 +47,7 @@
 #include <string.h>
 #include "starkernel/vm/kernel_hermes.h"
 #include "starkernel/vm/stadium.h"
+#include "starkernel/q48_16.h"
 
 static SkHermesMessage sk_hermes_msgs[SK_HERMES_MSG_MAX];
 
@@ -181,4 +182,24 @@ int sk_hermes_release(SkHermesMessage *msg) {
     return rc;
 }
 
+int sk_hermes_decay(SkHermesMessage *msg) {
+    uint64_t before, after;
+    StadiumCell *cell;
+
+    if (!msg || !msg->in_use || msg->stadium_cell < 0) return -1;
+
+    cell   = &stadium_cells()[msg->stadium_cell];
+    before = cell->header.heat;
+    after  = (uint64_t)q48_mul((q48_16_t)before, (q48_16_t)SK_HERMES_Q_DECAY);
+
+    cell->header.heat = after;
+
+    /* Task 2.5: the one site where consumed increments (and where held
+     * pays for it). SXXXVII.3: decay's delta is exact and in hand here. */
+    sk_hermes_consumed += before - after;
+    sk_hermes_held     -= before - after;
+
+    return 0;
+}
+
 #endif /* __STARKERNEL__ */