feat(trios-chat): swap pilot, five guards run t27c gen-rust output behind adapters

[dmitrii-f-t27]

Closes #1895

Part of #1812 (Trinity Secure Chat written once in .t27).

Stacked on #1820 and #1827 and contains their commits (workspace member, golden baseline, T27_PIN). Merge order: 1820, then 1827, then this PR. Own commits: 5cc43d7 (the swap) and ea88625 (merge of the updated 1827 branch, which adds the BR-IO-CHAT-07 baseline; no file of the swap changed).

What it does

Swaps 5 trios-chat guards to t27c gen-rust output. t27 SHA 5e5493cabbb99f21f8f9f6e3a00150fb3eb0d230, t27c t27c-bootstrap@0.5.2+5e5493cab (built from that tree).

File (crates/trios-chat/rings/...)	Spec (gHashTag/t27)	sha256 of t27gen/<stem>.rs = seal gen_hash_rust	Adapter, non-blank / non-comment lines (whole non-test part)	Mutation: original tests failing
CR-CHAT-01/src/key_package_expiry_guard.rs	PR 8187	8d2546de...a469	46 / 33	4 of 10
CR-CHAT-02/src/epoch_rollover_wraparound_guard.rs	PR 7647	3760df6b...f085	45 / 32	9 of 10
CR-CHAT-03/src/ratchet_tree_resolution_guard.rs	PR 8461	abcaf63f...907a	51 / 37	6 of 10
CR-CHAT-03/src/unmerged_leaves_bound_guard.rs	PR 8445	868119eb...d7db6	46 / 33	4 of 10
CR-CHAT-07/src/cover_decoy_ratio_governor.rs	PR 7969	27399ff1...835f	53 / 36	9 of 10

Time: about 8 minutes for the 5 files, starting from the scratch adapter drafts of 2026-10-10 (writing, composing, building, testing). Without drafts, expect more.

Layout (as in docs/chat/T27_PORT_CONVENTIONS.md, PR #1826):

• rings/<R>/src/t27gen/<stem>.rs: byte-identical gen-rust output, never edited; header "NOT LOWERED BY THIS BACKEND ... do not read this file as verified" kept.
• rings/<R>/src/<stem>.rs: original pub consts with original types (values read from t27gen), error enums with derives and #[non_exhaustive], docs, and the original #[cfg(test)] module byte for byte. The body is an adapter: match over the generated verdict back to Result<(), E>. mod t27gen is private.
• T27_PIN: 5 rows (file, spec, t27 SHA, built_by, sha256, seal file).
• The 4 ring Cargo.toml files get [lints.rust] unexpected_cfgs with check-cfg = ['cfg(feature, values("serde"))']: the generated derives carry #[cfg_attr(feature = "serde", ...)], and that lint fires during cfg evaluation, before the #[allow] on mod t27gen applies. The derive stays off. No root Cargo.toml / Cargo.lock change in this commit.

Checks on 5cc43d7 (local: cargo 1.94.0, rustc 1.94.0, repository Cargo.lock, --offline)

trios-chat-cr-chat-01  names = golden/test-names  476 passed 0 failed
trios-chat-cr-chat-02  names = golden/test-names  431 passed 0 failed (1 ignored doc-test, as baseline)
trios-chat-cr-chat-03  names = golden/test-names  520 passed 0 failed (1 ignored doc-test, as baseline)
trios-chat-cr-chat-07  names = golden/test-names  381 passed 0 failed
test modules vs 8b229e9489ee (sed from #[cfg(test)]): identical for all 5
t27c gen-rust <spec> | cmp - t27gen/<stem>.rs: silent for all 5
cargo test -p trios-chat: laws_hash 1/1, r_chat_guard 3/3, t27_pin 1/1 ("T27_PIN: 5 vendored file(s) checked")
e2e_chat_25: exit 0, 25 PASS lines = golden/e2e_pass.txt
falsifier_runner: exit 1 = golden/falsifier.exit, stdout = golden/falsifier.stdout
golden_vectors: stdout = golden/vectors.txt
warnings from the 5 adapter files: none; from t27gen/: none after the check-cfg entry

Mutation proof (one comparison flipped in each t27gen/ file, module tests run, file regenerated with t27c gen-rust, then cmp):

key_package_expiry_guard         now_secs > not_after -> <        FAILED 6 passed 4 failed; restored 10/10; cmp silent
epoch_rollover_wraparound_guard  rotation_count > MAX -> <        FAILED 1 passed 9 failed; restored 10/10; cmp silent
ratchet_tree_resolution_guard    leaf >= tree_size -> <           FAILED 4 passed 6 failed; restored 10/10; cmp silent
unmerged_leaves_bound_guard      leaf >= tree_size -> <           FAILED 6 passed 4 failed; restored 10/10; cmp silent
cover_decoy_ratio_governor       total < MIN_WINDOW -> >          FAILED 1 passed 9 failed; restored 10/10; cmp silent

Required checks (no-js-check, Test, Constitutional Enforcement, guard): see the checks of this PR.

The generated files are not hand-edited. Decision logic generated by t27c; no constant-time or equivalence claim beyond the tests listed.

L16 rationale: clippy -D warnings already fails at base 8b229e9 and ci.yml skips it; the generated code sits inside #[allow] mod t27gen.

Dmitrii Fedorov (@dmitrii-f-t27)

[tri-claw]

Summary by t27-bees

This PR replaces five hand-written chat guards with t27c gen-rust generated cores behind thin adapter layers. The generated code is vendored verbatim under t27gen/ (marked unverified), each original file becomes a private mod t27gen + a match translating the generated verdict to the original Result<(), E> error type, and a T27_PIN file records the t27 SHA, spec PR, and content hash for each guard. Four ring Cargo.toml files add an unexpected_cfgs lint allow for the #[cfg_attr(feature = "serde", ...)] derives that appear in generated code.

Worth a look

• crates/trios-chat/rings/CR-CHAT-01/src/key_package_expiry_guard.rs (adapter): The match on t27gen::verify_key_package_expiry(...) maps Ok(()) and Err(e) to the original KeyPackageExpiryError variants. If the generated verdict enum adds or renames variants, this match becomes non-exhaustive at compile time — but a silent logic mismatch (e.g., mapping two distinct generated errors to the same original variant) would not be caught.

• crates/trios-chat/rings/CR-CHAT-02/src/epoch_rollover_wraparound_guard.rs (adapter): Same pattern; the mutation test shows 9/10 original tests failed when the generated comparison was flipped, confirming the generated logic is exercised. However, the adapter’s From/Into conversions between generated and original error types could discard context (e.g., rotation_count vs MAX values) that callers rely on for diagnostics.

• crates/trios-chat/rings/CR-CHAT-03/src/ratchet_tree_resolution_guard.rs and unmerged_leaves_bound_guard.rs (adapters): Both guards live in the same ring and share the t27gen module layout. A change in the t27 spec that alters the generated function signatures (argument order, optionality) would require coordinated edits in both adapters; the current diff shows no shared helper, so drift is possible.

• crates/trios-chat/rings/CR-CHAT-07/src/cover_decoy_ratio_governor.rs (adapter): The generated file is the largest (72 lines). The adapter uses t27gen::verify_cover_decoy_ratio(...) and maps its Error enum. The #[non_exhaustive] on the original error enum means downstream crates cannot exhaustively match — if the adapter fails to cover a new generated variant, it will panic at runtime via the catch-all arm (if present) or fail to compile if the match is exhaustive.

• crates/trios-chat/T27_PIN (new file): This is the single source of truth for the vendored generated code. If a future t27c gen-rust run produces different output for the same spec+SHA (e.g., due to a t27c bug fix), the sha256 column will mismatch cmp - t27gen/<stem>.rs but the PR does not show a CI step that enforces this check on every build — only a local t27c gen-rust <spec> | cmp was run.

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