feat(portfolio): K3 — portfolio learning loop (shared verdict store, parity row 5) [skip-docs]

A single VerdictStore threaded through run_portfolio: a verdict available when
project k composes survives into project k+1's fold (method-spec §5 cross-project
threading). The optional verdict_dir is the portfolio-level expert inbox, read
before each fold (role split §3 Step 7 — the portfolio never writes a run's own
verdict back; §1/§6 — no self-contamination, only expert/seed verdicts cross).
compose_run_context gains an optional passed-in store (None = fresh; every
existing caller composes exactly as before).

Load-bearing (tests/test_portfolio_learning_loadbearing.py), 2 detach proofs +
control + §4.2 idempotency:
- cross-project threading: project 1's bundle seed survives into project 2's
  prompt via the shared store; detach (compose ignores the passed-in store,
  always fresh) -> red.
- portfolio inbox fold: a verdict_dir marker reaches the project's fold; detach
  (drop the run_portfolio merge) -> red; control (no verdict_dir) -> marker absent.
- double-merge idempotency: a verdict merged before every project folds exactly
  once (first-write-wins on id).

437->442 green, golden byte-exact, full gate clean (ruff + format + mypy strict).
run_s10.py and runs/ byte-untouched. README synced (test count, portfolio block,
load-bearing list). K2 re-entrancy test stays green — the shared store threads
verdict fold lines only, never bundle context markers.

[skip-docs]: no invariant changed (CLAUDE.md untouched); the run_portfolio and
compose_run_context docstrings + README carry the doc need.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RiTwaKLesgcwXx2mDviqpt

src/portfolio_optimiser_claude/run.py

@@ -61,7 +61,7 @@ class ComposedRunContext:
 
 
 def compose_run_context(
-    bundle_dir: Path, inbox_dir: Path | None = None, *, k: int
+    bundle_dir: Path, inbox_dir: Path | None = None, *, k: int, store: VerdictStore | None = None
 ) -> ComposedRunContext:
     """Compose the run context per §5: merge inbox → seed → fold — read-only.
 
@@ -69,10 +69,17 @@ def compose_run_context(
     fast ahead of any spend (§9). A missing/empty ``inbox_dir`` (or ``None``)
     leaves the composition identical to the no-inbox base. Nothing is ever
     written — the system reads the inbox, the expert writes it (§3 Step 7).
+
+    A passed-in ``store`` is used AS-IS (its existing verdicts survive the
+    merge, first-write-wins) — the §5 cross-project threading a portfolio pass
+    (K3) relies on: a verdict available at project k reaches project k+1's
+    fold. ``None`` (the single-run default) builds a fresh store, so every
+    existing caller composes exactly as before.
     """
     citations = build_citations(navigate_bundle(bundle_dir))
     ir_projection = load_validator_input(bundle_dir)
-    store = VerdictStore()
+    if store is None:
+        store = VerdictStore()
     inbox_merged = merge_inbox_into_store(store, inbox_dir) if inbox_dir is not None else 0
     seeded = seed_store_from_bundle(store, bundle_dir)
     context = fold_experience(