fix(figc4.6): Set Version 2.0 before Establish Data Link on the FRMR fallback (#45)

[M0LTE]

Fixes #45. Figure fix and its citation/prose bookkeeping in two independently revertable commits, following the #81 (#40) precedent.

What changed and why

On figc4.6 (Awaiting V2.2 Connection) the "FRMR received" column (t14_frmr_received) drew "Establish Data Link" before "Set Version 2.0". Establish Data Link (figc4.7) branches on the modulo and sends SABME while modulo 128 is still in effect, so the v2.0 fallback re-sent the very SABME the pre-v2.2 peer had just rejected with FRMR (§4.3.3.2): no progress against a v2.0 peer, and a modulo split against a v2.2 peer (the responder adopts 128 from the SABME while this station drops to 8).

The two boxes swap places on the column, so the arm now reads: SRT := Initial Default / T1V := 2 * SRT, Set Version 2.0, Set Layer 3 Initiated, Establish Data Link, then state 1 (Awaiting Connection). The re-establishment therefore goes out as a v2.0 SABM, which is what §6.3.2 ("a version 2.0 connection is made" once a pre-2.2 peer answers with FRMR) and §6.5 (reset "after receipt of a FRMR frame from a TNC using an older version of the protocol") intend, and what direwolf already does as an erratum.

Per file:

• sdl/DataLink_AwaitingV22Connection.graphml (commit 1): geometry of n66 (Establish Data Link, Subroutine call) and n68 (Set Version 2.0, Processing description) exchanged and edges e69..e72 re-pointed. Node ids, labels and d5 shape classes are unchanged; the column stays a straight top-down stack with no bend points, nothing else on the page moved, and a page-wide bounding-box check finds no overlaps.
• yaml/awaiting_v22_connection.sdl.yaml: regenerated by Packet.Sdl.Transcribe (ax25sdl main 181328b; the CI-pinned ff5bc7d produces byte-identical output). 25 transitions / 8 decisions as before; only t14's path order changes and no id changes, so the sidecar needed no re-keying.
• mmd/awaiting_v22_connection.g.mmd: regenerated by Packet.Sdl.CodeGen; the totality/determinism lint stays clean (120 arms, 13 subroutines, 8051 feasible valuations, 0 holes, 0 overlaps).
• svg/DataLink_AwaitingV22Connection.svg: regenerated by tools/render/render_all.py.
• yaml/awaiting_v22_connection.citations.yaml (commit 2): t14 annotated with an ERRATUM (figc4.6 t14 (FRMR fallback): 'Establish Data Link' precedes 'Set Version 2.0' — the v2.0 fallback re-establishes with SABME, not SABM #45) note and the §4.3.3.2 / §6.3.2 / §6.5 and direwolf references.
• doc/ax.25.2.3-draft.md (commit 2): row appended to "Changes from Version 2.2". No prose states the action order (§4.3.3.2, §6.3.2, §6.5 and the C4.6 captions were checked), so no section text changes. The embedded figc4.6 image files in the draft are not regenerated, the same deferral as fix(figc4.4 + figc4.5 + §4.4.2/§6.4.4): discard out-of-window duplicate I frames — X.25 2.4.6.4(a) guard, bound = negotiated k (#40) #81.

svgdiff (python3 tools/svgdiff/svg_diff.py main fix/45-frmr-fallback-order --all --merge-base --format markdown)

spec-sdl/v2.2-errata/data-link/svg/DataLink_AwaitingV22Connection.svg

nodes 80→80, edges 84→84, labels 23→23

	what	change
+	edge	Establish Data Link → 1 Awaiting Connection
+	edge	SRT <- Initial Default → Set Version 2.0
+	edge	Set Layer 3 Initiated → Establish Data Link
+	edge	Set Version 2.0 → Set Layer 3 Initiated
−	edge	Establish Data Link → Set Layer 3 Initiated
−	edge	SRT <- Initial Default → Establish Data Link
−	edge	Set Layer 3 Initiated → Set Version 2.0

The fourth removed edge, Set Version 2.0 → 1 Awaiting Connection, is missing from the list only because the SABM column carries an edge with the same signature and the tool de-duplicates by signature; a multiset diff of the graphml shows exactly four edges removed and four added, and the edge count is unchanged. The raw SVG diff is ten lines: the two boxes' transforms and their label positions.

Evidence

• ax25sdl golden trace traces/frmr-fallback-downgrades-to-sabm.trace.yaml: expects t14_frmr_received to emit SABM P=1 with version_2_2: false; marked expected_failure against the pre-fix figure.
• ax25sdl docs/explorer.md, figc4.6 t14 (FRMR fallback): 'Establish Data Link' precedes 'Set Version 2.0' — the v2.0 fallback re-establishes with SABME, not SABM #45 calibration row: awaiting-v22 seed, v20-frmr stub peer, timer-free progress on; the pre-fix figure emits SABME again and the link only comes up through figc4.2's T1 retry (4 steps).
• direwolf src/ax25_link.c frmr_frame at a231971: the state_5 arm runs set_version_2_0 (5044, "Erratum: Need to force v2.0. This is not in flow chart.") before establish_data_link (5046); the state_3/state_4 arm does the same at 5028/5030 ("FRMR can only be sent by v2.0").

ax25sdl follow-up: remove the expected_failure marker from traces/frmr-fallback-downgrades-to-sabm.trace.yaml and turn the #45 explorer calibration row clean (keep it firing on a pre-fix fixture)

Notes for review

• Trust the figure: only the two boxes figc4.6 t14 (FRMR fallback): 'Establish Data Link' precedes 'Set Version 2.0' — the v2.0 fallback re-establishes with SABME, not SABM #45 names moved. Set Layer 3 Initiated now sits between them, which is the order the issue suggests; Establish Data Link does not read Layer 3 Initiated, so the relative order of those two is behaviourally neutral.
• direwolf's other erratum on this arm (layer_3_initiated set in state 5 but cleared in state 1, its line 5047) is untouched and out of scope.

🤖 Generated with Claude Code

https://claude.ai/code/session_014qyx5dT8rmRTb8szT4SpEQ

[github-actions]

SVG figure changes (e4741fbe → 0073b33d)

spec-sdl/v2.2-errata/data-link/svg/DataLink_AwaitingV22Connection.svg

nodes 80→80, edges 84→84, labels 23→23

	what	change
+	edge	Establish Data Link → 1 Awaiting Connection
+	edge	SRT <- Initial Default → Set Version 2.0
+	edge	Set Layer 3 Initiated → Establish Data Link
+	edge	Set Version 2.0 → Set Layer 3 Initiated
−	edge	Establish Data Link → Set Layer 3 Initiated
−	edge	SRT <- Initial Default → Establish Data Link
−	edge	Set Layer 3 Initiated → Set Version 2.0

Interactive viewers — swipe, onion-skin, blink, and a clickable change list that zooms to each change — are attached to this run as the svg-figure-diff artifact: download, unzip, open the HTML.

_{Locally: python3 tools/svgdiff/svg_diff.py main HEAD --all --merge-base}