diff --git a/src/index_graph/interop.py b/src/index_graph/interop.py
new file mode 100644
index 0000000..bfa4f7c
--- /dev/null
+++ b/src/index_graph/interop.py
@@ -0,0 +1,90 @@
+"""Interop: index's context envelopes as organ-bundle interchange entries.
+
+The organ bundle is the shared spine gather, crucible, forum, learn, and index
+compose on. This module maps index's context envelopes (the budgeted,
+receipt-backed context packs) into that entry shape, so an index envelope can
+feed the agent loop, compose into forum's routing context, or back a learn
+lesson through the shared spine.
+
+Entry shape matches the proof-surface organ-bundle contract
+(entry_id, organ_id, receipt_kind, status, payload_sha256, summary, payload_ref).
+gather/src/gather/interop.py is the reference implementation.
+"""
+from __future__ import annotations
+
+import hashlib
+import re
+
+ORGAN = "index"
+SPINE_KIND = "index-context-envelope"
+STATUSES = frozenset({
+    "pass", "fail", "unverified", "warn", "needs-human", "not-applicable", "unknown",
+})
+_HEX = re.compile(r"^[0-9a-f]{64}$")
+_FIELDS = ("entry_id", "organ_id", "receipt_kind", "status", "payload_sha256",
+           "summary", "payload_ref")
+
+
+def _entry(entry_id: str, status: str, payload_sha256: str, summary: str, ref: str) -> dict:
+    return {
+        "entry_id": entry_id,
+        "organ_id": ORGAN,
+        "receipt_kind": SPINE_KIND,
+        "status": status,
+        "payload_sha256": payload_sha256,
+        "summary": summary[:160],
+        "payload_ref": ref,
+    }
+
+
+def envelope_entry(envelope: dict, *, entry_id: str = "index-envelope-1",
+                   ref: str = "index://context-envelope") -> dict:
+    """Map an index context-envelope output into an organ-bundle entry.
+
+    The envelope is a JSON dict (schema project-telos.context-envelope/v1)
+    produced by `index context --json` or the `index.context.envelope` MCP tool.
+    """
+    verification = envelope.get("verification_verdict", "UNVERIFIABLE")
+    selection = envelope.get("selection", {})
+    mode = selection.get("mode", "?") if isinstance(selection, dict) else "?"
+    retained = selection.get("retained_names", []) if isinstance(selection, dict) else []
+    repo_count = len(retained)
+
+    status = "pass" if verification == "MATCH" else "warn" if verification else "unverified"
+
+    # Use the envelope's own hash if present, else hash the canonical form
+    sha = envelope.get("envelope_sha256", "")
+    if not sha or not _HEX.match(sha):
+        import json
+        canonical = json.dumps(envelope, sort_keys=True, separators=(",", ":"))
+        sha = hashlib.sha256(canonical.encode("utf-8")).hexdigest()
+
+    summary = f"context-envelope: {repo_count} repos, mode={mode}, verdict={verification}"
+    return _entry(entry_id, status, sha, summary, ref)
+
+
+def map_entry(repo: str, *, n_repos: int = 1, map_sha: str = "",
+              entry_id: str = "index-map-1",
+              ref: str = "index://map") -> dict:
+    """Map an index map result into an organ-bundle entry."""
+    if not map_sha:
+        map_sha = hashlib.sha256(repo.encode("utf-8")).hexdigest()
+    summary = f"workspace map: {repo} ({n_repos} repos)"
+    return _entry(entry_id, "pass", map_sha, summary, ref)
+
+
+def validate_entry(entry: dict) -> bool:
+    """Validate one organ-bundle entry shape. Returns True if well-formed."""
+    if not isinstance(entry, dict):
+        return False
+    if set(entry.keys()) != set(_FIELDS):
+        return False
+    if entry["organ_id"] != ORGAN:
+        return False
+    if entry["receipt_kind"] != SPINE_KIND:
+        return False
+    if entry["status"] not in STATUSES:
+        return False
+    if not _HEX.match(entry.get("payload_sha256", "")):
+        return False
+    return True