Extract mastery threshold constants to shared file

[atbrace]

Problem

The threshold 85 appears in 3+ locations across the codebase: readiness calculator weak-topic filter, mastery utils display functions, and readiness level determination. The 65 ("approaching") threshold is similarly scattered. Magic numbers in multiple files will drift out of sync.

Solution

Extract into a shared constants file (e.g. src/lib/assess/constants.ts or src/lib/utils/constants.ts):

export const MASTERY_THRESHOLD = 85;      // "exam ready"
export const APPROACHING_THRESHOLD = 65;  // "approaching" readiness

Update all callsites to import from that file.

Files Affected

• src/lib/progress/calculator.ts
• src/lib/utils/mastery.ts
• src/components/ui/progress-indicator.tsx

References

• PR feat: exam readiness estimator with sound scoring methodology #49 review finding

[claude]

Issue Enrichment Report

Type

Chore/refactor - already labeled chore + enhancement. Both labels are appropriate; this is a pure code-quality refactor with no user-visible behavior change.

Scope & Alignment

In scope. Extracting shared constants is a standard maintainability practice and aligns with the project's structured, assessment-driven architecture.

Related Issues

• Duplicates: none found
• Overlaps with: Fix domain ID prefix collision in coverage-aware mastery calculation #53 - both touch src/lib/progress/calculator.ts; coordinate to avoid merge conflicts
• Blocked by: none
• Blocks: none

Acceptance Criteria

Criteria are missing from the issue. Proposed testable criteria:

• A single constants file (e.g. src/lib/constants.ts or src/lib/assess/constants.ts) exports named threshold constants
• grep -r " >= 85" src/ (excluding the new constants file) returns zero matches
• All existing tests pass without modification after the refactor
• TypeScript compilation succeeds with no new errors (pnpm tsc --noEmit)

Code Surface Area

Files likely touched:

The issue lists 3 files but the actual scope is larger - 8 files currently use hardcoded 85:

• src/lib/utils/mastery.ts - three >= 85 comparisons (lines 10, 20, 33)
• src/lib/progress/calculator.ts - >= 85 and >= 0.85 (lines 158, 333, 369)
• src/components/ui/progress-indicator.tsx - >= 85 (line 19)
• src/components/dashboard/DashboardHero.tsx - >= 85 (line 33)
• src/app/[exam]/assess/[domain]/AssessmentClient.tsx - >= 85 and >= 60 (lines 156-157)
• src/lib/llm/tool-handlers.ts - >= 85 (line 469)
• src/lib/utils/colors.ts - >= 85 and >= 60 (lines 28-29)
• src/lib/content/sidebar.ts - >= 85 (line 113)
• New file: src/lib/constants.ts (or src/lib/assess/constants.ts)

Effort estimate: medium (wider file spread than the issue implies, but changes are all mechanical find-and-replace + import additions)

Research Findings

Threshold discrepancy - action required before implementation: The issue states 65 is the "approaching" threshold but no 65 value exists in the codebase. The actual thresholds found are:

• 85 - "Exam Ready" / mastered
• 75 - intermediate band (in calculator.ts readiness level logic only)
• 60 - "Developing" lower bound (used in mastery.ts, progress-indicator.tsx, colors.ts, AssessmentClient.tsx)
• 0.85 - SQL-layer version of the mastery threshold (stored as 0-1 in DB, displayed as 0-100 in UI)

The constants file should cover all four values. The 0.85 SQL literal warrants special attention - it represents the same semantic threshold at a different scale and may need a separate MASTERY_THRESHOLD_DECIMAL constant or a derivation (MASTERY_THRESHOLD / 100).

Pattern to follow: src/lib/utils/mastery.ts is already the closest thing to a shared mastery utilities module. Placing constants in src/lib/assess/constants.ts (co-located with the assess engine) or src/lib/constants.ts (project-wide) would both be consistent with the existing src/lib/ structure.

Priority Assessment

Current P3-low is appropriate. This is a maintainability improvement with no functional impact, and no higher-priority work is blocked on it.

---

Automated enrichment by Claude - verify findings before implementation