docs(safety): de-stale SR-17 — reverse-direction non-BMP + lone-surrogate oracles now exist

[avrabe]

What

SR-17's verification-description (authored at the v0.31.0 traceability audit) lists the UTF-16 → UTF-8 reverse direction and lone-surrogate U+FFFD substitution as a carried gap — "covered structurally (LS-P-16) but not yet by a non-BMP runtime round-trip". The subsequent #272 async cross-encoding campaign closed that gap with runtime oracles, but the SR text was never updated. The result was an understated (phantom) gap in the safety record — the safe failure direction, but still a traceability defect that under-credits real verification.

This is a text-only correction to one existing verified SR. No links, artifacts, or statuses change.

Oracles that close the gap (all passing under wasmtime)

Oracle	Covers
test_sr17_utf16_to_utf8_supplementary_plane_transcoding	reverse-direction non-BMP round-trip — U+1F600 pair D83D DE00 → UTF-8 F0 9F 98 80
test_sr17_utf16_to_utf8_lone_high_surrogate_replacement	terminal lone high surrogate → U+FFFD EF BF BD
test_sr17_utf16_to_utf8_midstring_lone_surrogate_replacement	mid-string lone surrogate → U+FFFD
test_sr17_utf16_to_utf8_malformed_surrogate_matrix	malformed-input matrix
inc2_async_utf16_to_utf8_param_* (tests/async_cross_encoding.rs)	async path over the same shared decode/encode helpers

Verification

• adapter_safety SR-17 oracles: 8 passed / 0 failed; async non-BMP oracles: 44 passed / 0 failed.
• rivet validate: identical with and without this edit — 180 errors / 101 warnings / 0 broken cross-refs (the pre-existing left-side missing: feature/design-decision baseline; this edit changes no validation state).
• LS-N gate (run_ls_verification.py): 57 passed / 0 failed / 0 missing.

Scope

Touches only safety/requirements/safety-requirements.yaml — no Tier-5 source path, so no Mythos gate applies.

🤖 Generated with Claude Code

[github-actions]

LS-N verification gate

✅ 57/57 approved LS entries verified

	count
Passed (≥1 test, all green)	57
Failed (≥1 test failure)	0
Missing (no ls_*_NN_* test found)	0

_{Approved loss-scenarios.yaml entries are expected to have a
regression test named ls_<letter>_<num>_* (e.g. LS-A-11 →
ls_a_11_*). The gate runs each prefix via cargo test --lib --no-fail-fast and aggregates pass/fail/missing.}

Failed LS entries

(none)

Missing regression tests

(none)

_{Updated automatically by tools/post_verification_comment.py.
Source of truth: safety/stpa/loss-scenarios.yaml.}