feat: add model comparisons and sanitize session files

- Rename gamma to glm5 and model to minimax-m2.7
- Add model_comparison/ directory with head-to-head analyses
- Sanitize all session.jsonl files: remove absolute paths and usernames
- Remove __pycache__ artifacts
- Add .gitignore

qwen36/fuse/FINAL.md

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+Here's a summary of everything delivered:
+
+---
+
+## Deliverables
+
+### Files
+
+| File | Purpose |
+|------|---------|
+| `fused_softmax_topk.cu` | **Production kernel** — complete, correct, well-commented |
+| `fused_softmax_topk_v2.cu` | **Optimized kernel** — vectorized loads, warp-level merge |
+| `ANALYSIS.md` | **Full design analysis** — memory, complexity, comparisons |
+| `benchmark.cu` | **Correctness + perf harness** — CPU reference, timing, scaling |
+
+---
+
+### Architecture at a Glance
+
+```
+Grid:  B×T blocks (one per position)
+Block: 256 threads
+
+Phase 1:  max-reduction over V          → warp shuffle → shared mem
+Phase 2:  Σexp(xᵢ - max)                → warp shuffle → shared mem  
+Phase 3:  softmax + local top-K (regs)  → LOCAL_K=16 per thread
+Phase 4:  merge → shared min-heap       → warp-by-warp staging
+Phase 5:  sort + write-back             → thread 0, O(K²)
+```
+
+### Key Design Decisions
+
+| Constraint | Solution |
+|---|---|
+| **No full softmax in global mem** | Softmax values computed in registers, only top-K written out |
+| **Numerical stability** | Two-pass: find max first, then `exp(x - max)` |
+| **Large V (50k+)** | Grid-stride loops; each thread processes ~196 elements |
+| **Shared memory** | Min-heap (2KB) + warp staging (4KB) = 6.2KB total |
+| **Warp optimization** | `__shfl_xor_sync` for reductions (zero shared mem, ~15 cycles) |
+
+### Complexity (V=50257, K=256)
+
+| Metric | Value |
+|---|---|
+| Global reads | **12V = 2.4 MB** (3 passes, coalesced) |
+| Global writes | **8K = 2 KB** (output only) |
+| expf() calls | **2V = 100K** |
+| Bound | **Compute-bound** (expf throughput, not bandwidth) |
+
+### vs. Naive (softmax → topk)
+
+| Metric | Naive | Fused | Win |
+|---|---|---|---|
+| Global writes | 4V + 8K | **8K** | **~200× less** |
+| Peak memory | 4V + 8K | **8K** | **~200× less** |
+| Global reads | 8V | 12V | 0.67× (reads more) |
+| expf() calls | V | 2V | 0.5× (computes more) |
+
+**Net: The fused kernel trades 50% more reads for ~200× fewer writes.** For V=50K, this saves ~192 KB of global memory traffic per position — the write savings dominate.
+
+### Further Optimizations (documented in ANALYSIS.md §6)
+
+1. **Warp-level top-K merge** — reduce heap insertions from 4096 → 2048
+2. **FP16/BF16** — 2× bandwidth savings, acceptable precision loss
+3. **Vectorized loads (float4)** — already in v2, 4× fewer memory instructions
+4. **Persistent blocks** — for large B×T, better occupancy
+5. **Async copy (Hopper+)** — `__ldg()` for L2 cache reuse across passes
+6. **Single-pass online** — tracks running max, re-normalizes (complex, for V > 1M)