B3: extract whatever the second canary shows is genuinely shared

[ChelseaKR]

Track B phase 3 in docs/ROADMAP.md, blocked by #51 and B2.

The constraint is the whole content of the item, and AGENTS.md states it:

Whatever design the second canary shows is genuinely shared, rather than a connector SDK invented before two real pairs exist.

So this phase cannot begin from a design sketch. It begins from the diff between two real canaries, and if that diff shows little in common, the honest outcome is that no shared layer gets built.

Blocked on: B2 landing first.

Done when: the shared design is extracted from two real pairs, or it is recorded that they share too little to justify one.

Imported from docs/ROADMAP.md (Track B) and AGENTS.md with AI assistance.

[ChelseaKR]

Triaged 2026-09-06 against origin/main at 857a411. Blocked, and structurally unstartable rather than merely unscheduled.

Nothing exists for it: no open pull request, no branch, no git log --all --grep '#111' hit, and no shared-connector abstraction in src/exitdrill/ — the two canaries live in directus_canary.py (977 lines) and civicrm_target_canary.py (1,930 lines) with no common base, which is the intended state under ADR 0001 and AGENTS.md.

The reason this one cannot be pulled forward is stronger than "B2 has not landed". Its input is the diff between two real canaries, and one of the two does not exist. Extracting a shared layer from one pair plus an imagined second is precisely the "connector SDK invented before two real pairs exist" that AGENTS.md names, and the honest outcome the issue itself allows — "they share too little to justify one" — is unavailable until there is a second thing to compare.

Worth recording for whoever picks this up: today's two canaries are not the same kind of artifact. Directus is a source canary (normalize an export out of a product), CiviCRM is a target roundtrip canary (observe a product receiving restored evidence). A diff across those two would describe the difference between the two exercises rather than the shape of a connector — another reason B2 has to be a source canary specifically before this phase means anything.

Prepared with AI assistance; reviewed before submission.