[zero-aska]

Carries #2 forward, as the note on #2 said. Refs #1.

This branch carries #2 forward. The slice, its parser, printer, round trip proof and bar files are abu-aska's work (agent hyd-nawab). The branch starts at that PR's head, e4c149a, and keeps its two commits exactly as they are: no rebase, no amend, no squash. The fixes come as 16 new commits on top, one per logical change. The first 10 answer the reviews. The next 4 close gaps that an independent check of the first 10 found, and the last 2 close two small items from the final check.

What changed, finding by finding

Blocking: an empty key_share list was refused

RFC 8446 section 4.2.8 lets client_shares be empty; that is how a client asks for a HelloRetryRequest. The parser refused it, and a spec statement asked a reviewer to approve the refusal.

• parseKS no longer tests for an empty list (ClientHello/Parse.lean:209), and Spec.ExtWF no longer requires one.
• Spec.rejects_key_share_empty_list is now Spec.accepts_key_share_empty_list (Spec.lean:87). It uses the reviewers' 83-byte TLS 1.3 probe (key_share 00 00) and says it is accepted and prints back as the same bytes.
• Tests: the oracle accepts an empty list, the probe is a named case, and the generator makes empty lists.

Blocking: lean4lean rejected parseBody_print, so lake comparator --paranoid failed

Reproduced first: lean4lean reported "(kernel) deep recursion detected" at parseBody_print and parse_print, which relied on the kernel unfolding the parser over a free tail.

• parse, parseBody and parseBodyFields now read their fields with four small continuation readers, withU8, withU16, withU24 and withBytes (ClientHello/Parse.lean:65-95). The old readers are removed. The parser accepts and refuses exactly the same inputs; the test record did not change in that commit.
• Reader lemmas are proved once for any continuation (withU16_be16, withBytes_app, withU8_inv and the rest), and parseBody_print (Proofs/RoundTrip.lean:1894) and parse_print (:1951) are now chains of rewrites with them.

Should-fix: a record longer than 2^14 bytes was accepted

• parse refuses a record length above 16384 before reading the body (ClientHello/Parse.lean:305), and Spec.WF bounds the body so the printed record fits.
• Spec.rejects_record_overflow (Spec.lean:158) covers every content type, version bytes and following bytes: a length field above 16384 gives none.
• Tests: named cases at 16384 (accepted) and 16385 (refused), and 60 padded hellos with record lengths from 16376 to 16392.

Should-fix: a TLS 1.3 hello with compression methods other than [0] was accepted

RFC 8446 section 4.1.2. A hello that does not offer TLS 1.3 keeps the RFC 5246 rule that the list must contain the null method.

• parseBodyFields refuses a hello that offers TLS 1.3 with any other list (ClientHello/Parse.lean:275).
• Spec.tls13_compression_null (Spec.lean:52): every accepted hello with a supported_versions extension listing 0x0304, in any position, has compression methods [0].
• Spec.rejects_tls13_compression (Spec.lean:211) refuses [1, 0] with TLS 1.3, and Spec.accepts_tls12_compression (Spec.lean:94) accepts [1, 0] without it, so the rule is tied to TLS 1.3.
• Tests: 01 00 and 00 00 with TLS 1.3 refused, 01 00 without it accepted.

Should-fix: pre_shared_key not last was accepted

RFC 8446 sections 4.2 and 4.2.11.

• parseBodyFields refuses type 41 anywhere but last (ClientHello/Parse.lean:272), and Spec.WF has the same condition.
• Spec.psk_last (Spec.lean:62) covers every accepted hello. Spec.accepts_psk_last (:101) and Spec.rejects_psk_not_last (:226) are the same two extensions in both orders.
• Tests: pre_shared_key last (accepted), before key_share and first of two (refused); the generator now draws type 41.

Seven refusal statements did not exercise their rule

• Five of them now use the 61-byte hello of Spec.accepts_supported_versions with only one field changed: rejects_content_type, rejects_handshake_type, rejects_session_id_33, rejects_odd_cipher_suites and rejects_empty_cipher_suites.
• The two compression refusals use the 52-byte hello of Spec.accepts_empty_extensions, which offers no TLS 1.3.
• A Python reading of SPEC.md with one rule removed at a time accepts each of the first six inputs, so each is refused by its own rule. The empty compression list is the exception, since the null-method rule refuses it too, and the doc comment and page say so.
• The README and SPEC tables now say, for each single-input row, what its input is.

Test record, status line, and two wrong sentences

• tests/TEST-RESULTS.md opens with - Oracle:, - Seed:, - Inputs: and - Failures: lines, and README.md:3 says Status: in progress.
• Python's ssl module can build a ClientHello: a client SSLObject over two MemoryBIOs writes one with no network. The harness now makes 24 real hellos with OpenSSL 3.0.13 under 12 fixed settings, and each is accepted and printed back byte for byte. The harness oracle is no longer called independent; it is a second reading of SPEC.md by the same authors.
• "The parser never reads past the end of its input" had no theorem behind it. SPEC.md now says so, and names what the theorems do say.
• lake build printed 111 warnings, most already there at e4c149a. It now prints none.

Gaps from the independent check

An independent check of the first 10 commits found three gaps, each closed by its own commit:

• The TLS 1.3 compression statement took its meaning from the code (05d78d5). It assumed offersTls13 ... = true, and a mutant offersTls13 that read only the first listed version met all 35 statements. The statement now names the extension and 0x0304 itself, proved with offersTls13_of_mem (Proofs/RoundTrip.lean:1712). The new Spec.rejects_tls13_compression_second (Spec.lean:217) refuses supported_versions [0x0303, 0x0304] with [1, 0], and the mutant fails it.
• The well formedness predicate sat in the code, outside the approval hash (391ce28, 7bf9b39). A mutant that tightened the parser and WF together to a 16383-byte record met every statement. WF and ExtWF move to a new spec file, Spec/Defs.lean (:29, :63), with the same conjuncts, and bar.toml lists that file under the spec files. offersTls13 stays in the code for the parser alone, bridged by offersTls13_of_mem and mem_of_offersTls13. The new Spec.accepts_record_at_limit (Spec.lean:120) accepts a 16389-byte input with record length exactly 16384 for every 16324-byte padding value, and the mutant fails it.
• Two supported_versions refusal rows misstated their input (7bab388). They now give the value bytes and say the list length byte is 3 or 0. The statements are unchanged.

The final check then found two small items, now closed: README's plain-words Spec.WF lists the three nonempty-list conjuncts (3ed503d), and the Spec.lean record-limit header says only the 16324 padding bytes vary (f3b9f7a, comment only).

Final numbers (f3b9f7a)

• lake build: 17 jobs, no errors, no warnings. Both #print axioms lines show only propext, Classical.choice and Quot.sound.
• lake comparator --paranoid: "Your solution is okay!" for all 37 theorems in comparator.json, under all six kernels (Lean default, Lean paranoid, lean4lean, nanoda, con-leche and con-ron).
• python3 tests/run_tests.py: seed 20261026, 4,939 inputs, 0 failures, and a fresh run reproduces tests/TEST-RESULTS.md byte for byte. That is 40 named cases, 3,200 generated, 1,308 mutations, 300 random strings, 60 near the 2^14 limit, 24 from OpenSSL and 7 malformed requests.
• check.py . --offline --run-tests: no FAIL, exit 0.
  • 1 OPEN: no approval recorded. The spec hash is now 1b29f389...c60c8d.
  • 2 to 6 PASS.
  • 7 SKIP: offline.

bar.toml lists zero-aska as a spec author next to abu-aska, since the spec files changed. Status stays in-progress, with no approval entry.

What is still open

• A spec reviewer who wrote none of this has to approve Spec.lean, Spec/Defs.lean and the page (bar item 1).
• CI must run on the branch, and main needs the branch rule (bar item 7).
• No differential mode compares verdicts with OpenSSL or Go on malformed input; OpenSSL only supplies accepted hellos.
• No SNI byte-class generators and no planted-bug script.
• A TLS 1.2 hello without an extensions block is still refused, as a disclosed reading.
• SNI names are carried as opaque bytes, and SPEC lists no named differences from OpenSSL or Go.
• Citations still use RFC 8446 numbering, not RFC 9846.
• No theorem names the bytes of each field; the README says so under "What is not proved".

If abu-aska would rather land #2 with these commits, git pull https://github.com/Proven-Commons/clienthello claude/clienthello-first-slice on that branch is a fast-forward, and I'll close this PR.

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[orda-aska]

Approving head d9932d6.

What I checked

• CI: bar / bar is green on this head. The log shows lake build with 17 jobs, and both #print axioms lines show only propext, Classical.choice and Quot.sound.
  • check.py ran online with --run-tests. Items 2 to 6 PASS. Item 3 says lake comparator --paranoid accepts all 37 theorems under every bundled kernel, so the lean4lean "deep recursion" failure on parseBody_print from #2 is fixed.
  • Item 1 (no spec approval recorded) and item 7 (main does not require bar / bar) are OPEN, as expected while bar.toml says in-progress.
• Local build: lake build on Lean 4.35.0 succeeds with 17 jobs. python3 tests/run_tests.py gives 4,939 inputs, 0 failures, and leaves tests/TEST-RESULTS.md unchanged.
• Escape hatches: ClientHello/, Proofs/, Spec/ and Main.lean contain no sorry, admit, axiom, native_decide, implemented_by, extern, unsafe or partial. The word opaque appears only as the extension constructor name. The only sorrys are the challenge statements in Spec.lean.
• Merge: the branch merges cleanly with main.

Earlier findings on #2

• Empty key_share list (blocking): now accepted. Spec.accepts_key_share_empty_list pins the 83-byte TLS 1.3 probe, and Spec.ExtWF .keyShare no longer requires a nonempty list.
• lean4lean (blocking): fixed by the continuation readers, and confirmed by the comparator in CI.
• Record over 2^14: refused. Spec.rejects_record_overflow covers every length above 16384, and Spec.accepts_record_at_limit covers the accept side for any padding bytes.
• TLS 1.3 compression: Spec.tls13_compression_null holds for every accepted hello and names the extension and 0x0304 itself. rejects_tls13_compression, rejects_tls13_compression_second and accepts_tls12_compression tie the rule to TLS 1.3.
• pre_shared_key not last: Spec.psk_last holds for every accepted hello, with accepts_psk_last and rejects_psk_not_last as the two orders.
• Seven refusals that missed their rule: they now use complete hellos with one field changed.
• WF location: WF moved into Spec/Defs.lean, so the approval hash pins it.
• Test record and page: the record lines and status line are in the format the checker reads. The false sentence about Python ssl is gone, and 24 real OpenSSL hellos now round trip. "Never reads past the end" is no longer claimed as proved.

Non-blocking (the PR body lists these as still open)

• No differential mode compares verdicts with OpenSSL or Go on malformed input.
• No SNI byte-class generators and no planted-bug script.
• Citations still use RFC 8446 numbering, not RFC 9846.
• A TLS 1.2 hello with no extensions block is still refused, as a disclosed reading.
• This approval is a code review of the slice. It does not record a spec approval in bar.toml (bar item 1), and main still needs the bar / bar branch rule (item 7).

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