fix(rt): normalize singleton-array volatile pubkey writes

[Stevengre]

Summary

Fixes the projection/writeback path used by std::ptr::write_volatile::<[u8; 32]> after pointer casts from Pubkey in AccountInfo::assign-style code.

Changes:

• add singleton-array traversal/writeback context handling in rt/data.md
• add cancellation rules for SingletonArray + Field(0) + ConstantIndex(0) in both projection builders
• add integration reproducer write_volatile_pubkey_array.rs
• register the reproducer in test_integration.py
• document the blocker and evidence in docs/proof-issues/ISSUE-001-write-volatile-pubkey-array.md

Testing

Remote (zhaoji) standalone validation:

• uv --project kmir run -- kmir prove-rs kmir/src/tests/integration/data/prove-rs/write_volatile_pubkey_array.rs --start-symbol repro --proof-dir <tmp> --fail-fast
  • result: PASSED, nodes=3, pending=0, failing=0, stuck=0, terminal=2
• make test-integration TEST_ARGS="-k write_volatile_pubkey_array"
  • result: 1 passed

Reference RED baseline for the same leaf family is captured in ISSUE-001-write-volatile-pubkey-array.md.

Notes

• This addresses the semantic blocker family seen from test_process_close_account_multisig (leaf/node 132 shape).
• Known issue runtimeverification/solana-token#181 (uninitialized multisig OOB) remains explicitly out of scope for this patch.

[Stevengre]

@codex review

[Stevengre]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep it up!

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