Implement TREV-WP-0002 Stage 0 foundation: schemas, pure fold, golden Phase

Delivers the offline runnable specification foundation for the Trust Layer
(TSD §3-§6), not a hosted Trust Service:

- JSON Schemas for Phase Manifest, Ledger Entry, Extension Contract, and
  Conversion Attestation, encoding the Stage 0 working defaults (Q3 future
  license enum, Q6 single-currency Phases, Q8 required longstop_at).
- src/target_revenue: pure Outstanding Target fold, SHA-256 hash-chain
  verification, Ed25519 signing helpers, extension conformance checks
  (including a core-term-redefinition heuristic), and conversion detection
  that never requires an attestation document to determine conversion status.
- examples/phase-001: golden Phase package matching the concept doc's
  worked example, generated via scripts/generate_golden_phase.py so the
  hash chain is computed by the library itself, not hand-typed.
- 32 passing pytest tests covering manifest/ledger/extension conformance,
  tamper/reorder detection, and the full lifecycle fold to conversion.
- docs/adr/ADR-0001: proposed (not accepted) Stage 0 stack choice, per the
  WP-0002-T01 human-accept gate — implementation proceeded against the
  proposal as the workplan note permits, but the task stays open.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/target_revenue/conversion.py

@@ -0,0 +1,80 @@
+"""Conversion Event detection and Conversion Attestation generation.
+
+TSD §3.5 / PRD FR-7 / G6 / working default Q13: the Conversion Event is a
+pure fact about the Manifest + Ledger, never a discretionary declaration.
+`is_converted` and `conversion_status` below never require an attestation
+document to answer "has this Phase converted?" — the attestation, when
+generated, is evidence of an already-true fact, not its cause.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any
+
+from . import fold as fold_module
+from . import validation
+
+
+@dataclass(frozen=True)
+class ConversionStatus:
+    """Pure, offline-computable conversion status for a Phase."""
+
+    is_converted: bool
+    development_credit: float
+    remission_credit: float
+    outstanding_target: float
+    future_license: str
+
+
+def conversion_status(
+    manifest: dict[str, Any], entries: list[dict[str, Any]]
+) -> ConversionStatus:
+    """Compute conversion status directly from Manifest + Ledger.
+
+    No attestation document is consulted or required. This function is the
+    canonical "has this Phase converted" answer for any conformant tool.
+    """
+    result = fold_module.fold_phase(manifest, entries)
+    return ConversionStatus(
+        is_converted=result.is_converted,
+        development_credit=result.development_credit,
+        remission_credit=result.remission_credit,
+        outstanding_target=result.outstanding_target,
+        future_license=manifest["phase"]["future_license"],
+    )
+
+
+def generate_attestation(
+    manifest: dict[str, Any],
+    entries: list[dict[str, Any]],
+    conversion_timestamp: str,
+) -> dict[str, Any]:
+    """Build a Conversion Attestation document for an already-converted Phase.
+
+    Raises ValueError if the Phase has not actually converted (Outstanding
+    Target > 0) — an attestation must never assert a conversion that hasn't
+    happened, and must never be required to make one happen.
+    """
+    status = conversion_status(manifest, entries)
+    if not status.is_converted:
+        raise ValueError(
+            "cannot generate a Conversion Attestation: Outstanding Target "
+            f"is {status.outstanding_target}, not 0"
+        )
+
+    last_entry = entries[-1] if entries else None
+    checkpoint = last_entry["id"] if last_entry else "GENESIS"
+
+    attestation = {
+        "phase": manifest["phase"]["id"],
+        "milestone_release": manifest["phase"]["milestone_release"]["name"],
+        "conversion_timestamp": conversion_timestamp,
+        "future_license": status.future_license,
+        "final_development_credit": status.development_credit,
+        "final_remission_credit": status.remission_credit,
+        "final_outstanding_target": status.outstanding_target,
+        "ledger_checkpoint": checkpoint,
+    }
+    validation.validate_conversion_attestation(attestation)
+    return attestation