chore: connect upgrade-sk and PR #64/#65/#66 to current main without tree changes #70

Problem

upgrade-sk and current main have no common ancestor. Pull requests #64, #65, and #66 all target upgrade-sk, so GitHub cannot compute their relationship to the maintained line reliably.

Verified refs before repair:

• main: 168fd5d8bef5301a8f849d95492e815a38af8afb
• upgrade-sk: c7ce61ffcd757916a981b4892b6d21b6b2dcb461
• fix(tests,#7225): document SK 1.78 planning-paradigm decision + re-model samples/Plans + update Skip reasons #64 (c699-work): a1eb200e6d017910e6e4d51f4e1a2bb69e025b4b
• feat(samples,#7225): SK 1.78 plan JSON intermediate format + PlanJsonHelpers helper #65 (fix/7225-sk178-plan-helper): 941ead746629bcdef7ab8536ed29800b21959399
• fix(tests,#7225): rewrite MultiConnectorTests for SK 1.78 + PlanJsonHelpers xUnit suite #66 (fix/c716-7225-multiconnector-tests-rewrite): 4588c478b2d86ff2d0ecbe7591f4af34456d11e1
• common base of fix(tests,#7225): document SK 1.78 planning-paradigm decision + re-model samples/Plans + update Skip reasons #64/feat(samples,#7225): SK 1.78 plan JSON intermediate format + PlanJsonHelpers helper #65/fix(tests,#7225): rewrite MultiConnectorTests for SK 1.78 + PlanJsonHelpers xUnit suite #66: a95e92f37708354f15861f4f7d11faa9d8d0307c

Preservation-safe repair

Connect the histories with explicit two-parent ours merges:

1. On upgrade-sk, record current main as a second parent while preserving the complete upgrade-sk tree.
2. On each PR head, record the repaired upgrade-sk tip as a second parent while preserving that PR's complete tree.
3. Push all four updates as ordinary fast-forwards. No rebase, cherry-pick, conflict auto-resolution, or force-push.

A local proof run produced byte-identical trees:

All four repaired tips resolve 168fd5d8bef5301a8f849d95492e815a38af8afb as their merge-base with main.

Acceptance

• git merge-base main upgrade-sk succeeds.
• fix(tests,#7225): document SK 1.78 planning-paradigm decision + re-model samples/Plans + update Skip reasons #64, feat(samples,#7225): SK 1.78 plan JSON intermediate format + PlanJsonHelpers helper #65, and fix(tests,#7225): rewrite MultiConnectorTests for SK 1.78 + PlanJsonHelpers xUnit suite #66 each have a merge-base with current main.
• Every repaired branch keeps the exact tree ID of its pre-repair tip.
• All remote updates are fast-forwards; no force-push.
• GitHub recomputes fix(tests,#7225): document SK 1.78 planning-paradigm decision + re-model samples/Plans + update Skip reasons #64/feat(samples,#7225): SK 1.78 plan JSON intermediate format + PlanJsonHelpers helper #65/fix(tests,#7225): rewrite MultiConnectorTests for SK 1.78 + PlanJsonHelpers xUnit suite #66 without the no-common-ancestor blocker.

This structural repair is intentionally separate from #69. The supported-SDK matrix modernization remains the next sequential change after ancestry is restored.