docs(tech-debt): mark CORE-01 (S1) borrow-checker Phase-3 DONE — closes #177

[hyperpolymath]

Summary

• Refresh docs/TECH-DEBT.adoc CORE-01 row: ledger listed Slices C' / D / ref-to-ref binding as residual, but those landed (PRs feat(borrow): CORE-01 ref-to-ref binding (#177 pt3) — let r2 = r / r = s alias the borrow-graph #395 / feat(borrow): CORE-01 Slice C' loop soundness — 2-iteration check on while/for (Refs #177) #396 / feat(borrow): CORE-01 Slice D (#177 pt3) — reject @linear capture by closure at borrow check #397).
• Flip the Stage D ASCII status from ACTIVE to CLOSED.
• Mark the row CLOSED 2026-05-30; remaining residual is scoped exclusively to ADR-022 (Polonius origin/region variables) which is a separate, ADR-gated workstream filed at docs/decisions/0022-polonius-origin-variables.adoc (PR docs(adr): ADR-022 — origin variables + Polonius-style loan solver (Refs #177) — surgical refile of #398 #407).

Why now

#177 was the issue tracking CORE-01 Phase-3 (borrow-graph validation, S1). The stated scope — adding graph validation plus regression fixtures under tests/ — has shipped:

• Code: lib/borrow.ml:1635-1715 documents pt1 + pt2 (return-escape + &mut parser surface) + pt3 Slices A (NLL last-use) / B (flow-sensitive re-assignment) / C-light (CFG-join for ExprHandle/ExprTry) / C' (loop soundness) / D (linear-capture by closure) + ref-to-ref binding.
• Tests: test/test_e2e.ml "E2E Borrow Graph" suite — 28 hermetic regression tests (covering each landed slice with positive + anti-regression cases).
• Slices that landed since the ledger was last updated: feat(borrow): CORE-01 ref-to-ref binding (#177 pt3) — let r2 = r / r = s alias the borrow-graph #395 (ref-to-ref binding), feat(borrow): CORE-01 Slice C' loop soundness — 2-iteration check on while/for (Refs #177) #396 (Slice C' loop soundness), feat(borrow): CORE-01 Slice D (#177 pt3) — reject @linear capture by closure at borrow check #397 (Slice D linear-capture), fix(borrow): whole-place assignment clears move-record (Refs #177) #399 (whole-place assignment clears moves), fix(borrow): self-assign guard + return-escape coverage for ref-to-ref (Refs #177, follow-up to #395) #400 (self-assign guard + return-escape coverage for ref-to-ref).
• ADR-022 (docs(adr): ADR-022 — origin variables + Polonius-style loan solver (Refs #177) — surgical refile of #398 #407): Polonius origin/region variables — architectural change to the type system. M1–M4 migration plan in the ADR; lexical checker is the merge oracle through M3.

Build oracle

Local toolchain has an unrelated cross-installation OCaml conflict (astring.cmxa from opam vs system stdlib.cmxa); using CI-on-main as oracle instead.

CI green on main at 4f0f3ca7 (2026-05-30 15:19Z) with all CORE-01 work present.

Test plan

• CI green on this branch
• No code in the diff; doc-only change (no behaviour impact)
• Closes #177 link resolves on merge

Closes #177.

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