Add design docs for achievable status fix and course description popups change artifacts

docs/superpowers/specs/2026-03-27-achievable-status-fix-design.md

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+# Fix: "Achievable" status ignores credit sharing with achieved specs
+
+**Date:** 2026-03-27
+**Type:** Bugfix
+
+## Problem
+
+`determineStatuses()` marks specializations as "achievable" based solely on per-specialization upper bounds (`computeUpperBounds`), which ignore credit sharing between specializations. A spec can show "achievable" (upper bound >= 9) even when it's infeasible alongside the already-achieved higher-priority specs because shared courses have committed their credits elsewhere.
+
+**Reproduction scenario:**
+- 11 courses selected, Fall 1 open
+- Priority: CRF > STR > LCM > MGT
+- LCM upper bound = 10 (from spr1-collaboration, spr3-M&A, fall1-managing-change, fall3-corporate-governance)
+- CRF + STR achieved, consuming credits from spr3 and fall3
+- LCM shows "Achievable" but `checkFeasibility([all courses], ['CRF', 'STR', 'LCM'])` is infeasible for all S2 choices
+- Selecting Managing Change for Fall 1 achieves MGT (priority 4) instead of LCM (priority 3)
+
+## Root Cause
+
+`determineStatuses()` in `optimizer.ts:146-185` checks only:
+1. Whether the spec is in the achieved set
+2. Whether the required course gate passes
+3. Whether `computeUpperBounds` >= 9 (per-spec, ignoring sharing)
+
+It never checks whether the spec is actually feasible alongside the achieved set.
+
+## Fix
+
+In `determineStatuses()`, after a non-achieved spec passes the upper bound check, add a feasibility check: call `checkWithS2(selectedCourseIds, [...achieved, specId])`. If infeasible, mark as `unreachable` instead of `achievable`.
+
+### Changes
+
+**`optimizer.ts` — `determineStatuses` function:**
+- After the upper bound check passes (currently falls through to `statuses[spec.id] = 'achievable'`), add:
+  ```ts
+  const testSet = [...achieved, spec.id];
+  const feasResult = checkWithS2(selectedCourseIds, testSet);
+  if (!feasResult.feasible) {
+    statuses[spec.id] = 'unreachable';
+    continue;
+  }
+  ```
+- No new parameters needed — `selectedCourseIds` is already passed to the function.
+
+### What doesn't change
+
+- No new status types — reuses existing `unreachable`
+- No UI changes — `unreachable` already renders correctly with grey styling
+- `computeUpperBounds` unchanged — still used for credit bar display
+- `AllocationResult` type unchanged
+- `checkWithS2` helper already exists in the same file
+
+### Test updates
+
+- Add a test for the bug scenario: given the specific course selection and CRF > STR > LCM > MGT ranking, verify LCM status is `unreachable` (not `achievable`) when CRF and STR are achieved
+- Existing test `marks achievable when required course is in open set` should be unaffected (uses all-open sets with no achieved specs, so feasibility check passes trivially)
+
+### Performance
+
+14 specializations total, at most ~10 non-achieved specs to check. Each check is a small LP solve. Negligible overhead.