std79 exerciser campaign: 27/27 legs clean, two real D. bugs found (FABRIC-3.md §XII.4)

Completed the FORTH-79 standard-dictionary cross-ISA exerciser campaign: all
9 identities (zuse, rajames/bob, 00-06) x all 3 architectures (amd64,
aarch64, riscv64), 27 legs total. No crashes, no heap corruption across the
full run -- real-world validation that the WIREBIND use-after-free fix
(commit 9142dda, FABRIC-3.md SXIII) holds under genuine multi-cycle load,
not just the synthetic repro used to verify it.

Cross-identity parity is perfect: 0 diffs across all 9 identities on each
architecture. Two real bugs found in double-precision (D.) output, reported
per this project's standing rule (report, don't fix without being asked):

- M* on a negative operand -> D. reports DOUBLE-OVERFLOW, universally
  across all three architectures (engine-level bug, not arch-specific).
- D+ on two negative doubles -> D. reports DOUBLE-OVERFLOW on aarch64
  only; amd64 and riscv64 both correctly print -2. cell_t width confirmed
  64-bit on all three (ruled out as the cause); exact mechanism still open.

Also fixed a test-harness timing issue (run_identities.sh): the retry
budget for USE-after-attach was too tight for boots with several live VMs
already accumulated, causing false "FAILED to USE" verdicts on identities
that actually succeeded a few seconds later. Widened the budget and
switched to smaller per-boot batches (2-3 identities) as the reliable
pattern for this shape of campaign.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EXieurDfDSsDFdnSyusuWo

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