What this lens asks: what kind of market am I in, and does my strategy's edge survive it? Regime — trending vs ranging, risk-on vs risk-off, bull vs bear vs sideways — is the cross-cutting filter that decides whether a given edge is currently live or currently inverted. Trend-following and breakout systems make their money in trending regimes and bleed via whipsaw in ranging ones; mean-reversion does the reverse. A strategy is implicitly a bet that a particular market behavior persists, so when the regime changes, the behavior stops and the edge can flip sign.

This is a lens (synthesis) node, not the regime catalog. The object-level taxonomy and identification methods — defining trending/ranging conditions, risk-on/off, the bull/bear/sideways cycle, and the indicators used to label them — live in Macro & Intermarket Analysis (domain #903) and are not duplicated here. What this branch adds is the consequence:

• Why Strategies Are Regime-Dependent (the synthesis doc in this section) — the mechanism by which edges are conditional on regime, why a backtested Sharpe is a regime-weighted average that hides large dispersion, and the discipline this implies: identify the regime before selecting a strategy, and reduce size or stand aside when the regime is ambiguous or transitioning.

Honest caveat: regimes are cleanly labelable mainly in hindsight; live identification lags and is noisy, and over-fitting a strategy to the most recent regime is itself a failure mode.

For the Augustus swing agent: Augustus already consumes a Market Regime signal — this lens explains why that input should gate whether a setup is greenlit, not merely annotate it.

Related: [[why-strategies-are-regime-dependent]] · Macro & Intermarket Analysis (#903) · the companion lenses [[timeframe-and-holding-period]] and [[volatility-environment]].