session-memory: distributor base + Artifact (WP-0007 T01)

distribute/base.py: Artifact dataclass + Distributor protocol + idempotent
BEGIN/END snippet markers (upsert_block replaces a pattern's block in place so
re-distribution doesn't duplicate) + agnostic markdown body rendering from
SolutionPattern fields. BaseDistributor honours per-flavor body/target hints.
8 new tests; suite 110/110.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

session_memory/distribute/__init__.py

@@ -0,0 +1,9 @@
+"""Distribute phase (PRD §6.4) — render approved Solution Patterns into per-flavor
+artifacts. Mirror of the collector design: agnostic core, thin distributor edges.
+
+    base.py      Artifact + Distributor protocol + idempotent snippet markers (T01)
+    claude.py    CLAUDE.md snippet distributor (T02)
+    codex.py     AGENTS.md snippet distributor (T03)
+    grok.py      native instruction distributor (T03)
+    __main__.py  `python -m session_memory.distribute` (T05)
+"""

session_memory/distribute/base.py

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+"""Distributor base — Artifact, the Distributor protocol, and idempotent markers
+(PRD §6.4 FR-X1; T01).
+
+A **distributor** turns one agnostic :class:`SolutionPattern` into a per-flavor
+:class:`Artifact` (a target path + a snippet of content). Everything flavor-neutral
+lives here; each flavor adapter (T02/T03) only supplies its target filename and may
+override the rendered body using the pattern's ``rendering_hints``.
+
+Snippets carry stable ``BEGIN/END`` markers keyed on the pattern id, so
+re-distributing a pattern **updates its block in place** instead of duplicating it
+— the property that lets Distribute run repeatedly (HITL) without drift.
+"""
+
+from __future__ import annotations
+
+import re
+from dataclasses import dataclass
+from typing import Any, Optional, Protocol, runtime_checkable
+
+from ..curate.schema import SolutionPattern
+
+
+@dataclass
+class Artifact:
+    """A proposed per-flavor rendering of a pattern (FR-X1/FR-X3 — proposed, not applied)."""
+
+    flavor: str
+    target_path: str        # repo-relative file the snippet belongs in (e.g. "CLAUDE.md")
+    pattern_id: str
+    content: str            # the marker-wrapped snippet block
+
+
+@runtime_checkable
+class Distributor(Protocol):
+    flavor: str
+    target_path: str
+
+    def render(self, pattern: SolutionPattern) -> Artifact: ...
+
+
+# --- idempotent snippet markers ---------------------------------------------
+
+_MARK = "helix-forge pattern"
+
+
+def begin_marker(pattern_id: str) -> str:
+    return f"<!-- BEGIN {_MARK}:{pattern_id} -->"
+
+
+def end_marker(pattern_id: str) -> str:
+    return f"<!-- END {_MARK}:{pattern_id} -->"
+
+
+def wrap_block(pattern_id: str, body: str, version: str = "") -> str:
+    """Wrap a rendered body in stable BEGIN/END markers."""
+    ver = f" v{version}" if version else ""
+    return f"{begin_marker(pattern_id)}{ver}\n{body.strip()}\n{end_marker(pattern_id)}"
+
+
+def upsert_block(doc_text: str, pattern_id: str, block: str) -> str:
+    """Insert or replace a pattern's marked block within a document (idempotent)."""
+    pat = re.compile(
+        re.escape(begin_marker(pattern_id)) + r".*?" + re.escape(end_marker(pattern_id)),
+        re.DOTALL,
+    )
+    if pat.search(doc_text):
+        return pat.sub(block, doc_text)
+    sep = "" if doc_text.endswith("\n\n") or not doc_text else "\n\n"
+    return f"{doc_text}{sep}{block}\n"
+
+
+# --- agnostic body rendering ------------------------------------------------
+
+def render_markdown_body(pattern: SolutionPattern) -> str:
+    """Default flavor-neutral snippet body from the agnostic pattern fields."""
+    label = "Avoid" if pattern.polarity == "problem" else "Prefer"
+    lines = [f"### {pattern.name}", "", pattern.problem.strip(), ""]
+    if pattern.resolutions:
+        lines.append(f"**{label}:**")
+        for r in pattern.resolutions:
+            detail = f" — {r.detail}" if r.detail else ""
+            lines.append(f"- {r.summary}{detail}")
+            for step in r.steps:
+                lines.append(f"  - {step}")
+    return "\n".join(lines).strip()
+
+
+def hint(pattern: SolutionPattern, flavor: str, key: str, default: Any = None) -> Any:
+    """Read a per-flavor rendering hint, falling back to ``default``."""
+    return (pattern.rendering_hints.get(flavor) or {}).get(key, default)
+
+
+class BaseDistributor:
+    """Shared distributor: renders the agnostic body, honouring a ``body`` hint
+    override and a ``target`` hint, then wraps it in idempotent markers."""
+
+    flavor: str = ""
+    target_path: str = ""
+
+    def __init__(self, flavor: Optional[str] = None, target_path: Optional[str] = None) -> None:
+        if flavor is not None:
+            self.flavor = flavor
+        if target_path is not None:
+            self.target_path = target_path
+
+    def body(self, pattern: SolutionPattern) -> str:
+        return hint(pattern, self.flavor, "body") or render_markdown_body(pattern)
+
+    def target(self, pattern: SolutionPattern) -> str:
+        return hint(pattern, self.flavor, "target") or self.target_path
+
+    def render(self, pattern: SolutionPattern) -> Artifact:
+        block = wrap_block(pattern.id, self.body(pattern), pattern.version)
+        return Artifact(flavor=self.flavor, target_path=self.target(pattern),
+                        pattern_id=pattern.id, content=block)