feat(strategy): add opt-in strategy marketplace with copy-trading (#285)

ASSUMPTIONS.md

@@ -0,0 +1,63 @@
+# Assumptions
+
+Documented, reasonable assumptions made while implementing features, so a
+reviewer can override any of them without archaeology.
+
+---
+
+## Issue #285 — Strategy Marketplace / Opt-In Copy-Trading
+
+1. **`strategyConfig` serializes exactly `{ strategyName, targetAllocations?,
+riskCeiling? }`** — the three keys `src/agent/loop.ts` actually reads.
+   `riskTolerance` stays personal to the follower and is never copied.
+
+2. **The risk-free rate for Sharpe is 0**, exposed as
+   `STRATEGY_RISK_FREE_RATE`. Stating it explicitly beats a hidden non-zero
+   assumption. Sourcing a live rate is deferred.
+
+3. **Metric recompute interval defaults to 6 h**
+   (`STRATEGY_METRICS_INTERVAL_MS`), matching `config.protocolRisk.intervalMs`.
+   Figures derive from hourly snapshots, so a faster cadence buys nothing.
+
+4. **Publishing does not require an eligible track record.** A publisher simply
+   does not appear on the leaderboard until they have one. This keeps publishing
+   and ranking independent.
+
+5. **`GOAL_TRACKING` is not publishable.** It is driven by the publisher's own
+   `SavingsGoal` target and date — personal figures that mean nothing to a
+   follower and would have to be copied for the strategy to work at all.
+   Followers with their own goal already get goal precedence.
+
+6. **`POST /strategies/publish` accepts an explicit `strategyConfig`, and
+   snapshots the caller's `User.rebalanceStrategy` / `User.strategyConfig` when
+   it is omitted.** Nothing in `src/` currently _writes_ those User columns, so
+   an explicit body is the only way the feature is usable today; the snapshot
+   path is there for when a "set my strategy" endpoint lands.
+
+7. **`TARGET_ALLOCATION` weights must sum to 100.** Followers inherit them
+   verbatim, so a set that does not sum to 100 would quietly under- or
+   over-allocate someone else's funds.
+
+8. **DEVIATION from the plan's signature:** `computeStrategyMetrics` takes an
+   input object with a separate `firstObservedAt` rather than
+   `(points, now?)`. The window governs the _return statistics_; the track
+   record governs _trust_. Deriving the track record from the windowed series
+   would make the 30-day window structurally incapable of ever reaching a
+   30-day track record (its oldest sample sits ~30 days back and floors to 29),
+   leaving the 30-day leaderboard permanently empty.
+
+9. **Follower notifications dispatch once per follower**, not once per event,
+   because a webhook consumer needs to know whose agent is affected — matching
+   the per-user payload convention of `alert_rule.triggered`. A strategy with
+   many followers therefore produces a proportional webhook fan-out.
+
+10. **Unfollow tolerates an orphaned follow.** When a publisher deletes their
+    account, `onDelete: SetNull` leaves the follower with no strategy id to
+    name. `POST /strategies/:id/unfollow` releases the caller's active follow
+    when its `publishedStrategyId` is null, regardless of the id supplied. It
+    only ever touches the caller's own single active row, so the looser match is
+    not a privilege boundary.
+
+11. **The metrics job computes for unpublished strategies too**, so re-publishing
+    is ranked immediately instead of waiting up to a full interval. The
+    marketplace query, not the job, applies the `isPublished` filter.

docs/DOCUMENTATION_INDEX.md

@@ -1,3 +1,3 @@
 # Documentation Index - Issue #23: Vault Events Persistence
 
 ## Quick Navigation
@@ -9,6 +9,7 @@
 - **[IMPLEMENTATION_DETAILS.md](IMPLEMENTATION_DETAILS.md)** - Deep dive into implementation
 - **[API_REFERENCE.md](API_REFERENCE.md)** - Complete backend endpoint reference
 - **[TAX_REPORT.md](TAX_REPORT.md)** - Tax reporting & FIFO cost-basis lot tracking (#284)
+- **[STRATEGY_MARKETPLACE.md](STRATEGY_MARKETPLACE.md)** - Strategy marketplace / opt-in copy-trading: metric formula, eligibility gate, privacy & custody boundaries (#285)
 
 ### For DevOps/Deployment
 
@@ -272,9 +273,9 @@
 ### For Code Review
 
 1. CODE_STRUCTURE.md - Architecture
-3. IMPLEMENTATION_DETAILS.md - Technical details
-4. Review src/stellar/events.ts - Code review
-5. Review tests - Test coverage
+2. IMPLEMENTATION_DETAILS.md - Technical details
+3. Review src/stellar/events.ts - Code review
+4. Review tests - Test coverage
 
 ---