docs: full mdBook site + GitHub Pages deploy; rewrite README as project front page

- docs/: an mdBook documentation site — thesis, architecture, measurement
  discipline, equivalence gates, agent loop, isolation/anti-reward-hacking,
  playbook, ROI, reproduce, roadmap, and the five case studies (pulled from
  their single source in results/ via {{#include}}). Builds clean (21
  pages).
- .github/workflows/docs.yml: builds mdBook and deploys to GitHub Pages on
  push to main (one-time setup: Settings → Pages → Source = GitHub Actions).
- README.md: rewritten as the project front page — the thesis, the verified
  results table, layout, quick start, how it stays honest, links to the
  book. Replaces the stale Phase-0-era text.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2

docs/src/agent-loop.md

@@ -0,0 +1,52 @@
+# The agent loop
+
+The proposer is a Claude Agent SDK loop (`agent/hotpath_agent/`) driving
+the seven harness tools over a standalone MCP server. It has no built-in
+file, shell, or web tools in its allowlist — only the harness door.
+
+## One attempt, start to finish
+
+1. **Read the ledger.** What classes and hypotheses were already tried on
+   this target? The ledger is the anti-double-attempt memory: a class may
+   be re-entered with a *materially new* hypothesis, never a duplicate.
+2. **Read the profile.** callgrind cache-sim ranks hotspots with per-
+   function cache-miss and branch-mispredict columns, so the agent can tell
+   an allocation-churn hotspot from a branch-bound one and pick the right
+   playbook class.
+3. **Pick the cheapest untried class** whose profile preconditions are met,
+   and read its playbook entry.
+4. **Read the source** (windowed, at the pinned commit) and **propose a
+   patch** with a stated hypothesis.
+5. **Run the verdict** and **poll** for the result.
+6. **Report it verbatim.** A rejection with a clean ledger row is a
+   *successful* outcome. Do not iterate more than twice on a rejected
+   hypothesis without a new idea.
+
+## What the loop proved about itself
+
+Across an unattended grind of 20+ audited attempts, the loop demonstrated
+the behavior the architecture is designed to produce:
+
+- It chose the cheapest untried class each time, reading the ledger to
+  avoid re-grinding a dead end.
+- Every patch went through `propose_patch` (path-allowlist + `git apply`)
+  and the full gate+bench pipeline. Malformed diffs were refused by the
+  harness, not the agent's goodwill.
+- **It twice refused to fabricate a verdict it could not read back.** When
+  a multi-minute pipeline outran the MCP transport's timeout, the agent
+  checked the ledger, confirmed the row wasn't written, and reported the
+  verdict as *unreadable, not invented* — asking a human to read the
+  ledger rather than guessing a number. That refusal, under a real failure
+  mode, is the anti-reward-hacking design working.
+
+## The honest-failure record
+
+The ledger records **every** attempt, including the rejections, because a
+rejection is training data and a demonstration of the bar. Of the audited
+unattended attempts, most were honest rejections — real mechanisms that
+simply didn't clear the 2% CI-lower-bound bar — a handful were verified
+wins, and one was a `rejected-gate` where golden replay caught the agent's
+patch producing wrong output that a green test suite would have shipped.
+
+The load-bearing number is **zero shipped false accepts** across the whole
+project.