Completion-moment stats: longest streak and the Module Reward count, once derivable

[maximsan]

Corrected 2 Sep 2026 against main: both inputs now exist, so this ticket is unblocked. #141 landed (closed) — the active-day set is stored and the streak derives from it. And the card model now does distinguish the five module collectibles: CollectibleUnlock carries exactly one of lessonId / moduleId, and the bank holds 32 lesson-unlocked and 5 module-unlocked cards — the Module Reward count is a pure derivation, with no content-model change owed. The screen still shows the substitutions ('Cards collected' / 'Day streak', course_completion_screen.dart), so the ask stands.

Parent

Follow-up owed by #120's build notes: the two completion-moment stats #128 shipped as substitutions, upgraded to what the spec asked for once their inputs exist.

What to build

The Foundations completion moment shows three stats. Two shipped as flagged substitutions (#120 build notes) because their spec form was not derivable at the time:

1. "Day streak" → longest streak. The spec asks for the learner's longest streak. Once the active-day set is wired (Tracer bullet: a completed lesson records its day and the streak everywhere derives from the day set #141 and the §10 fold), longest streak is a pure derivation over stored days — compute it, show it, and label it honestly ("Longest streak"). No new field: deriving is the point, and a stored copy is exactly the Sync scope and the persisted data model #14-shaped decision the build notes refused to make silently.
2. "Cards collected" → the Module Reward count. The spec names "every Field Guide" — the five module collectibles — but the card model does not distinguish them from lesson cards. Settle the distinction by derivation (e.g. the module-reward ids are already known content-side), not by a new stored marker; if it needs a content-model change, that goes back to the extractor's owner as a question first.

Both changes are label + derivation swaps on the existing screen; the moment's structure, firing rule and hand-off are untouched.

Acceptance criteria

• The completion moment shows the longest streak, derived purely from the active-day set — verified against a day set holding a broken streak (e.g. 5 then gap then 3 shows 5)
• The Module Reward stat counts exactly the module collectibles, derived, with the derivation's source named in the code
• No new stored field anywhere; a reset leaves nothing behind
• The screen's stat labels match what they actually show
• Unit tests cover the longest-streak derivation (gap cases) and the Module Reward derivation; the existing widget tests are updated to the new labels
• The two Keep Sharp on Today, and the Foundations completion moment #120 build notes are answered with a pointer to this ticket's PR

Blocked by

• Tracer bullet: a completed lesson records its day and the streak everywhere derives from the day set #141 — the active-day set the longest-streak derivation reads.

---

Vocabulary note (22 Aug 2026). This ticket was written when the five module collectibles were called Field Guides. CONTEXT.md now rules them Module Rewards and lists Field Guide under Avoid (#106, swept in #222). The title and criteria above are updated; the quoted phrase "every Field Guide" is left as-is, because it quotes the design spec as it was written. Nothing this ticket asks for changes — only the name of the thing being counted.

---

Built — PR #557. What verified each box: the longest-streak cases (5-gap-3 reads 5, three-then-five reads 5, an abandoned history keeps its best, a freeze-covered miss joins one run rather than two) are in streak_engine_test.dart, and the property test's day-by-day oracle now derives the longest run independently and agrees. The Module Reward count is checked against the real bank in collected_module_rewards_test.dart — 5 of 37, and 5 for a full collection. Nothing is stored: both come off the day set and the owned-collectible set a reset already clears. The screen was driven on a simulator with a nine-day run behind a gap and a live three-day one, and showed 9.