diff --git a/docs/weird_machine_conservation_law.md b/docs/weird_machine_conservation_law.md
index 1fbf511a..c9c07955 100644
--- a/docs/weird_machine_conservation_law.md
+++ b/docs/weird_machine_conservation_law.md
@@ -448,3 +448,56 @@ Each problem needs its own admissibility check matching its structure:
 No universal check. The ManifoldShortcut framework's "problem-specific
 admissibility" (from the 5-way attack refinement) is confirmed by
 this linearity analysis.
+
+## Capstone: The Octagon Principle
+
+### "If you can't fit a square peg in a triangle hole, turn them both into octagons."
+
+- **Square peg** = nonlinear data (Sidon set, combinatorial structure)
+- **Triangle hole** = linear tool (eigenvalue spectrum, SLOS, QR)
+- **They don't fit** = Attack 5: linear coherence can't detect nonlinear structure
+- **Octagon** = the embedding (matrix) compatible with BOTH
+
+The octagon has MORE sides than either — it's richer, not simpler.
+The matrix carries the nonlinear property (Sidon structure) AND has a
+linear spectrum (eigenvalue decomposition). Both data and tool are
+transformed into the octagon (matrix) where they interface.
+
+### This IS the Observerless Observer Protocol
+
+The invariant (nonlinear property) survives the projection (matrix
+embedding) because the spectral signature is preserved. The observer
+(linear tool) and the observed (nonlinear data) meet at the octagon
+level — the matrix — where the invariant is detectable.
+
+DNA is the octagon carrier: structurally linear (compatible with the
+pipeline) but carrying nonlinear meaning (compatible with the problem).
+The p-adic valuations are the octagon's corners — linear (prime
+factorization) but carrying nonlinear information (set structure).
+
+### What the Session Proved (Measured)
+
+| Problem | Octagon works? | Why |
+|---------|----------------|-----|
+| Sidon sets | YES (4/4) | Pairwise-sum matrix → eigenvalue degeneracy = spectral signature |
+| GW ringdown | Partial (1.5x) | Mode coupling matrix → spectrum works for signal, noise is residual |
+| Text | NO (3.088 b/B) | Co-occurrence matrix → spectrum doesn't capture language structure |
+| Graph coloring | YES (known) | Adjacency matrix → Hoffman bound: chromatic ≥ max eigenvalue + 1 |
+
+### The Principle
+
+The octagon works when the nonlinear property HAS a linear spectral
+signature. It fails when the property is genuinely non-spectral.
+
+The conservation law governs INFORMATION (can't reduce it).
+The octagon reduces COMPUTATION (finds the embedding where linear
+tools apply). These are different axes:
+- Compression: reduce information → blocked by conservation law
+- Computation: reduce cost → enabled by the octagon embedding
+
+### The Honest Split
+
+- Compression: dead (conservation law, measured across 8 branches)
+- Computation shortcut: alive (octagon embedding, measured for Sidon)
+- The pipeline's real value: find the octagon for each problem
+  (the matrix embedding where the nonlinear property becomes spectral)