diff --git a/conformance/fixtures/valid/composition.kpack/PACK.yaml b/conformance/fixtures/valid/composition.kpack/PACK.yaml
new file mode 100644
index 0000000..f0b0d25
--- /dev/null
+++ b/conformance/fixtures/valid/composition.kpack/PACK.yaml
@@ -0,0 +1,4 @@
+name: composition-fixture
+version: 2026.04.18
+domain: test/conformance
+author: KP Conformance Suite
diff --git a/conformance/fixtures/valid/composition.kpack/claims.md b/conformance/fixtures/valid/composition.kpack/claims.md
new file mode 100644
index 0000000..eb77ed1
--- /dev/null
+++ b/conformance/fixtures/valid/composition.kpack/claims.md
@@ -0,0 +1,23 @@
+<!-- KP:1 — Knowledge Pack Format
+Claims: - [ID] assertion {confidence|type|evidence|date|depth|nature} context
+  Positions 5-6 optional. Verbose named-field syntax also accepted.
+Types: o=observed r=reported c=computed i=inferred
+Depth: assumed | investigated | exhaustive (optional, position 5)
+Nature: judgment | prediction | meta (optional, position 6; omitted=factual)
+Relations: →supports ⊗contradicts ⊗!error ⊗~tension ←requires ~refines ⊘supersedes ↔see_also
+Files: evidence.md=sources history.md=past entities.md=graph composition.yaml=references
+-->
+---
+pack: composition-fixture | v: 2026.04.18 | domain: test/conformance
+confidence: simple | normalized
+---
+
+# Composition Fixture
+
+> Composition pack fixture. References other packs via `composition.yaml` — see `minimal-fixture` and `typical-fixture`. Evidence lives in those referenced packs, not here. This pack carries composition-context narrative only.
+
+## Composition Context
+
+This fixture exercises the composition-pack path in the conformance runner. It has `composition.yaml` present, no `evidence.md`, and only narrative content in `claims.md` — no dense claim bullets to cite evidence for.
+
+A composition pack SHOULD contain claim bullets when its composition context warrants them (e.g., a meeting pack with claims about the meeting itself). This fixture intentionally omits them to prove the minimum-shape case.
diff --git a/conformance/fixtures/valid/composition.kpack/composition.yaml b/conformance/fixtures/valid/composition.kpack/composition.yaml
new file mode 100644
index 0000000..a2502d2
--- /dev/null
+++ b/conformance/fixtures/valid/composition.kpack/composition.yaml
@@ -0,0 +1,25 @@
+type: meeting-prep
+
+meeting:
+  date: 2026-04-18T10:00:00-04:00
+  duration: 30m
+  participants:
+    - Alice
+    - Bob
+  context: >
+    Conformance test fixture — demonstrates a valid composition pack
+    structure with no evidence.md. All knowledge lives in referenced
+    packs; this pack only declares the composition.
+
+agenda:
+  - topic: Minimal pack coverage
+    reference: minimal-fixture
+    talking_points:
+      - Confirm frontmatter parsing
+      - Walk through a single-claim pack
+
+pre_load:
+  - minimal-fixture
+
+on_demand:
+  - typical-fixture
diff --git a/conformance/fixtures/valid/maximal.kpack/signatures.yaml b/conformance/fixtures/valid/maximal.kpack/signatures.yaml
new file mode 100644
index 0000000..5248396
--- /dev/null
+++ b/conformance/fixtures/valid/maximal.kpack/signatures.yaml
@@ -0,0 +1,14 @@
+algorithm: SHA-256
+pack_id: "0b3c1f9a-4d7e-4a1c-9f2b-3e4a5b6c7d8e"
+pack_name: maximal-fixture
+pack_version: "2026.04.04-rev2"
+pack_hash: "0000000000000000000000000000000000000000000000000000000000000000"
+files:
+  PACK.yaml: "1111111111111111111111111111111111111111111111111111111111111111"
+  claims.md: "2222222222222222222222222222222222222222222222222222222222222222"
+  evidence.md: "3333333333333333333333333333333333333333333333333333333333333333"
+sealed_at: "2026-04-18T10:00:00Z"
+sealed_by: capture-client
+parent:
+  version: "2026.04.04-rev1"
+  pack_hash: "4444444444444444444444444444444444444444444444444444444444444444"
diff --git a/conformance/grammar/kp-signatures.schema.json b/conformance/grammar/kp-signatures.schema.json
index f1aa575..87bc528 100644
--- a/conformance/grammar/kp-signatures.schema.json
+++ b/conformance/grammar/kp-signatures.schema.json
@@ -2,65 +2,111 @@
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "$id": "https://kp.dev/schemas/kp-signatures-v1.json",
   "title": "KP:1 signatures.yaml Schema",
-  "description": "JSON Schema for the signatures.yaml integrity manifest in a KP:1 knowledge pack. Provides cryptographic hashes and optional signing for integrity verification.",
+  "description": "JSON Schema for the signatures.yaml integrity manifest in a KP:1 knowledge pack. Aligned with ARCHIVE.md §4 (v0.7.3+).",
   "type": "object",
-  "required": ["algorithm", "files"],
+  "required": ["algorithm", "pack_hash", "files", "sealed_at", "sealed_by"],
   "additionalProperties": false,
   "properties": {
     "algorithm": {
       "type": "string",
-      "enum": ["sha-256", "sha-384", "sha-512"],
-      "description": "Hash algorithm used for all file digests."
+      "enum": ["SHA-256"],
+      "description": "Hash algorithm. Currently only SHA-256 (future-proofed for upgrades)."
     },
-    "signed_at": {
+    "pack_id": {
       "type": "string",
-      "format": "date-time",
-      "description": "ISO 8601 timestamp of when the hashes were computed and optionally signed."
+      "description": "Stable pack identity across versions. OPTIONAL in the schema for backward compatibility with pre-documentation archives; new archives SHOULD include it."
+    },
+    "pack_name": {
+      "type": "string",
+      "description": "Optional self-describing pack name (equal to PACK.yaml name). Enables receipts and relay indexing without a second file read."
+    },
+    "pack_version": {
+      "type": "string",
+      "description": "Optional self-describing pack version (equal to PACK.yaml version). Enables receipts without a second file read."
+    },
+    "pack_hash": {
+      "type": "string",
+      "pattern": "^[a-f0-9]{64}$",
+      "description": "Pack content hash computed per ARCHIVE.md §3 (lowercase hex SHA-256 digest, 64 characters)."
     },
     "files": {
       "type": "object",
       "additionalProperties": {
         "type": "string",
-        "pattern": "^[a-f0-9]+$",
-        "description": "Hex-encoded content hash for the file."
+        "pattern": "^[a-f0-9]{64}$"
+      },
+      "propertyNames": {
+        "not": { "const": "signatures.yaml" }
       },
       "minProperties": 1,
-      "description": "Map of file paths (relative to pack root) to their hex-encoded content hashes. At minimum should include PACK.yaml and claims.md."
+      "description": "Map of NFC-normalized relative file paths (with / separator) to their lowercase hex SHA-256 digests. MUST NOT include the root-level signatures.yaml itself (enforced via propertyNames)."
+    },
+    "sealed_at": {
+      "type": "string",
+      "format": "date-time",
+      "description": "ISO 8601 UTC timestamp of sealing (e.g., 2026-04-12T14:30:00Z)."
     },
-    "signing_key": {
+    "sealed_by": {
+      "type": "string",
+      "description": "Identifier of the sealing system (e.g., capture-client, analysis-service)."
+    },
+    "parent": {
       "type": "object",
-      "required": ["type", "public_key"],
+      "required": ["version", "pack_hash"],
       "additionalProperties": false,
       "properties": {
-        "type": {
+        "version": {
           "type": "string",
-          "enum": ["ed25519", "ecdsa-p256", "rsa-4096"],
-          "description": "Key algorithm."
+          "description": "Parent pack's version string from its PACK.yaml."
         },
-        "public_key": {
+        "pack_hash": {
           "type": "string",
-          "description": "Base64-encoded public key."
+          "pattern": "^[a-f0-9]{64}$",
+          "description": "Parent pack's pack_hash (lowercase hex)."
         },
-        "key_id": {
-          "type": "string",
-          "description": "Optional key identifier for key management systems."
+        "merge_parents": {
+          "type": "array",
+          "items": {
+            "type": "object",
+            "required": ["version", "pack_hash"],
+            "additionalProperties": false,
+            "properties": {
+              "version": {
+                "type": "string",
+                "description": "Additional parent's version string."
+              },
+              "pack_hash": {
+                "type": "string",
+                "pattern": "^[a-f0-9]{64}$",
+                "description": "Additional parent's pack_hash (lowercase hex)."
+              }
+            }
+          },
+          "description": "Additional parent references for branch-merge lineage. OPTIONAL; absent in single-parent archives."
         }
       },
-      "description": "Signing key reference. Required when a signature is present."
+      "description": "Parent version reference. Absent for v1 of a pack; present for v2 and later."
     },
     "signature": {
-      "type": "string",
-      "description": "Base64-encoded cryptographic signature over the canonical hash manifest."
-    }
-  },
-  "allOf": [
-    {
-      "if": {
-        "required": ["signature"]
+      "type": "object",
+      "required": ["method", "value", "key_id"],
+      "additionalProperties": false,
+      "properties": {
+        "method": {
+          "type": "string",
+          "enum": ["ed25519", "hmac-sha256", "rsa-pss-sha256"],
+          "description": "Signing method identifier."
+        },
+        "value": {
+          "type": "string",
+          "description": "Base64-encoded (standard, padded) signature over the signing payload defined in ARCHIVE.md §4.2."
+        },
+        "key_id": {
+          "type": "string",
+          "description": "Opaque key identifier for locating the verification key."
+        }
       },
-      "then": {
-        "required": ["signing_key", "signed_at"]
-      }
+      "description": "Optional digital signature. When present, all three sub-fields are REQUIRED."
     }
-  ]
+  }
 }
diff --git a/conformance/run.py b/conformance/run.py
index 720df06..7e4811c 100644
--- a/conformance/run.py
+++ b/conformance/run.py
@@ -39,6 +39,7 @@
 
 SCRIPT_DIR = Path(__file__).resolve().parent
 SCHEMA_PATH = SCRIPT_DIR / "grammar" / "kp-pack.schema.json"
+SIGNATURES_SCHEMA_PATH = SCRIPT_DIR / "grammar" / "kp-signatures.schema.json"
 FIXTURES_DIR = SCRIPT_DIR / "fixtures"
 EXAMPLES_DIR = SCRIPT_DIR.parent / "examples"
 
@@ -48,6 +49,7 @@
     "verbose-claims.kpack",
     "mixed-syntax.kpack",
     "maximal.kpack",
+    "composition.kpack",
 ]
 INVALID_ORDER = [
     "no-rosetta.kpack",
@@ -79,6 +81,7 @@
 }
 
 _schema_cache = None
+_signatures_schema_cache = None
 
 
 def schema():
@@ -89,6 +92,14 @@ def schema():
     return _schema_cache
 
 
+def signatures_schema():
+    global _signatures_schema_cache
+    if _signatures_schema_cache is None:
+        with open(SIGNATURES_SCHEMA_PATH) as f:
+            _signatures_schema_cache = json.load(f)
+    return _signatures_schema_cache
+
+
 def _stringify_dates(obj):
     """Convert datetime.date objects from PyYAML back to ISO strings."""
     if isinstance(obj, (datetime.date, datetime.datetime)):
@@ -135,7 +146,17 @@ def validate_pack(pack_dir: Path) -> list[Err]:
     pack_yaml_path = pack_dir / "PACK.yaml"
     claims_path = pack_dir / "claims.md"
     evidence_path = pack_dir / "evidence.md"
-    for p in (pack_yaml_path, claims_path, evidence_path):
+    composition_path = pack_dir / "composition.yaml"
+    signatures_path = pack_dir / "signatures.yaml"
+
+    # Composition packs MAY omit evidence.md (SPEC.md §2,
+    # "Composition-pack File Requirements"). claims.md remains required.
+    is_composition = composition_path.exists()
+    required_files = [pack_yaml_path, claims_path]
+    if not is_composition:
+        required_files.append(evidence_path)
+
+    for p in required_files:
         if not p.exists():
             errs.append(Err("parse", f"missing {p.name}"))
     if errs:
@@ -152,6 +173,25 @@ def validate_pack(pack_dir: Path) -> list[Err]:
     except jsonschema.ValidationError as e:
         errs.append(Err("schema", e.message))
 
+    # ── signatures.yaml: validate against its schema (if present) ──
+    if signatures_path.exists():
+        try:
+            sigs = _stringify_dates(yaml.safe_load(signatures_path.read_text()))
+        except yaml.YAMLError as e:
+            errs.append(Err("signatures", f"signatures.yaml parse error: {e}"))
+        else:
+            if sigs is None:
+                errs.append(Err("signatures", "signatures.yaml is empty"))
+            else:
+                try:
+                    jsonschema.validate(
+                        sigs,
+                        signatures_schema(),
+                        format_checker=jsonschema.FormatChecker(),
+                    )
+                except jsonschema.ValidationError as e:
+                    errs.append(Err("signatures", f"signatures.yaml: {e.message}"))
+
     # ── claims.md: Rosetta header ──
     text = claims_path.read_text()
     rosetta = re.match(r"<!-- KP:(\d+)\s", text)
@@ -187,8 +227,10 @@ def validate_pack(pack_dir: Path) -> list[Err]:
     if isinstance(pc, dict) and "scale" in pc and pc["scale"] != fm_scale:
         errs.append(Err("SC-10", f"scale '{fm_scale}' != PACK.yaml '{pc['scale']}'"))
 
-    # ── evidence.md: extract defined evidence IDs ──
-    ev_ids = set(re.findall(r"^## (E\d+)", evidence_path.read_text(), re.MULTILINE))
+    # ── evidence.md: extract defined evidence IDs (empty set if absent) ──
+    ev_ids: set[str] = set()
+    if evidence_path.exists():
+        ev_ids = set(re.findall(r"^## (E\d+)", evidence_path.read_text(), re.MULTILINE))
 
     # ── claims.md: parse claim blocks ──
     # A claim block starts with `- [C###]` or `- **[C###]**` and includes
diff --git a/spec/ARCHIVE.md b/spec/ARCHIVE.md
index cfd3a71..afa82c4 100644
--- a/spec/ARCHIVE.md
+++ b/spec/ARCHIVE.md
@@ -165,6 +165,14 @@ This section defines the schema for `signatures.yaml`, resolving SPEC.md §2's "
 # Hash algorithm (currently only SHA-256; future-proofed for upgrades)
 algorithm: SHA-256
 
+# Stable pack identity across versions (OPTIONAL for legacy archives;
+# SHOULD be present in new archives — see "Required fields" below)
+pack_id: "0b3c1f9a-4d7e-4a1c-9f2b-3e4a5b6c7d8e"
+
+# Self-describing receipts (OPTIONAL; mirrors PACK.yaml name/version)
+pack_name: "solar-energy-market"
+pack_version: "2026.03.18"
+
 # Pack hash — computed per §3
 pack_hash: "a1b2c3d4e5f6..."
 
@@ -196,12 +204,16 @@ signature:
 | Field | Type | Format |
 |-------|------|--------|
 | `algorithm` | string | Algorithm identifier. Currently `SHA-256`. |
+| `pack_id` | string | Stable identity of the pack across versions. A UUID is RECOMMENDED. Two sealed archives MUST share the same `pack_id` if and only if they represent versions of the same logical pack. |
+| `pack_name` | string | Self-describing copy of `PACK.yaml.name`. Enables receipts and indexing without loading the manifest. |
+| `pack_version` | string | Self-describing copy of `PACK.yaml.version`. Same rationale as `pack_name`. |
 | `pack_hash` | string | Lowercase hex-encoded SHA-256 digest (64 characters). |
 | `files` | map\<string, string\> | Keys: NFC-normalized relative paths with `/` separator. Values: lowercase hex SHA-256 digests. MUST NOT include `signatures.yaml`. |
 | `sealed_at` | string | ISO 8601 UTC timestamp (e.g., `2026-04-12T14:30:00Z`). |
 | `sealed_by` | string | Identifier of the sealing system (e.g., `capture-client`, `analysis-service`). |
 | `parent.version` | string | Parent pack's version string from its PACK.yaml. |
 | `parent.pack_hash` | string | Parent pack's `pack_hash` (lowercase hex). |
+| `parent.merge_parents` | array\<object\> | OPTIONAL. Additional parent references for branch-merge lineage. Each entry has the same shape as `parent` itself (`version` + `pack_hash`). Absent in single-parent archives. |
 | `signature.method` | string | Signing method identifier: `ed25519`, `hmac-sha256`, or `rsa-pss-sha256`. |
 | `signature.value` | string | Base64-encoded (standard, padded) signature over the signing payload. |
 | `signature.key_id` | string | Opaque key identifier for locating the verification key. |
@@ -215,9 +227,13 @@ signature:
 | `files` | Always | |
 | `sealed_at` | Always | |
 | `sealed_by` | Always | |
+| `pack_id` | New archives | SHOULD be present in archives sealed against v0.7.5 or later. Schema accepts absence for backwards compatibility with archives sealed before `pack_id` was documented. Readers MUST tolerate its absence. |
+| `pack_name` | Never | OPTIONAL; aids self-describing receipts. |
+| `pack_version` | Never | OPTIONAL; aids self-describing receipts. |
 | `parent` | When version > 1 | Absent for the first version of a pack |
 | `parent.version` | When `parent` is present | Both sub-fields are REQUIRED when the `parent` block exists |
 | `parent.pack_hash` | When `parent` is present | |
+| `parent.merge_parents` | Never | OPTIONAL; populated only when a version results from merging two or more lineages |
 | `signature` | When signing is configured | Optional; depends on deployment |
 | `signature.method` | When `signature` is present | All three sub-fields are REQUIRED when the `signature` block exists |
 | `signature.value` | When `signature` is present | |
diff --git a/spec/CHANGELOG.md b/spec/CHANGELOG.md
index 9567fd4..7757ed5 100644
--- a/spec/CHANGELOG.md
+++ b/spec/CHANGELOG.md
@@ -5,6 +5,28 @@
 
 ---
 
+## v0.7.5 — 2026-04-18
+
+**Signatures schema alignment + composition-pack file requirements.**
+
+### Added
+- **`pack_id` in `signatures.yaml`** — Stable pack identity across versions, emitted by current sealers and used by relays. Documented in ARCHIVE.md §4 with a prose MAY/SHOULD policy for backwards compatibility (schema accepts absence; new archives SHOULD include it). `pack_name` and `pack_version` also documented as optional self-describing receipts.
+- **`parent.merge_parents`** — Optional array inside the `parent` block for branch-merge lineage. Each entry has the same `version`/`pack_hash` shape as `parent` itself. Documents a latent capability declared in the sealer implementation so the refreshed schema does not reject valid merge-lineage archives.
+- **Composition-pack file requirements** — New subsection in SPEC.md §2 listing the file-presence rules for composition packs: `composition.yaml` REQUIRED, `claims.md` REQUIRED (intentionally minimal, about the composition context only), `evidence.md` OPTIONAL. Cross-references `spec/COMPOSITION.md` for semantics.
+- **Signatures schema validation in the conformance runner** — `conformance/run.py` now validates any `signatures.yaml` it finds against `kp-signatures.schema.json`, with `jsonschema.FormatChecker` enabled so declared formats (`date-time`) are actually enforced. Empty-file and YAML parse errors are surfaced with friendly messages. Previously the runner was silent on signatures.
+- **Fixture: `composition.kpack`** — Valid-pack fixture demonstrating the composition-pack minimum shape (composition.yaml present, no evidence.md, prose-only claims.md).
+- **Fixture: `signatures.yaml` on `maximal.kpack`** — Exercises the signatures schema with a populated `parent` block and the optional `pack_name`/`pack_version` fields.
+
+### Changed
+- **`kp-signatures.schema.json`** — Regenerated to match ARCHIVE.md §4 (v0.7.3+ shape). Required fields are now `algorithm`, `pack_hash`, `files`, `sealed_at`, `sealed_by`. Optional: `pack_id`, `pack_name`, `pack_version`, `parent` (with `version` + `pack_hash` + optional `merge_parents`), `signature` (with `method` + `value` + `key_id`). Previous pre-v0.7.3 fields (`signed_at`, `signing_key`, `signature` as a flat string) removed. Schema root closed with `additionalProperties: false`, mirroring the manifest-schema pattern. The `files` map now enforces "MUST NOT include signatures.yaml itself" via `propertyNames`, not prose alone.
+- **`conformance/run.py`** — `validate_pack()` detects composition packs (those with `composition.yaml`) and skips the `evidence.md` presence check for them. Evidence-ID extraction now tolerates a missing `evidence.md` (empty set rather than exception). `signatures.yaml` is validated against the new schema when present, with `FormatChecker` enabled so `format: date-time` on `sealed_at` is actually enforced.
+
+### Fixed
+- **Schema-vs-impl drift** — The prior `kp-signatures.schema.json` required fields (`signed_at`, `signing_key`, `signature` as a flat string) that neither the sealer (kp-forge) nor the relay (kp-packs) have produced or consumed since v0.7.3. Any current sealed archive would have failed schema validation. Aligned.
+- **Composition-pack validation hole** — Packs with `composition.yaml` and no `evidence.md` (valid per `COMPOSITION.md` design) were being rejected by the conformance runner for the missing-file reason. No longer.
+
+---
+
 ## v0.7.4 — 2026-04-16
 
 **Manifest extension lane — standardizes where experiments belong without widening the core schema.**
diff --git a/spec/SPEC.md b/spec/SPEC.md
index e112904..9af69aa 100644
--- a/spec/SPEC.md
+++ b/spec/SPEC.md
@@ -192,6 +192,20 @@ A Knowledge Pack is a directory with a conventional name ending in `.kpack/` (re
 
 The primary file is a **complete reasoning surface** AND a **navigation map** to everything else.
 
+### Composition-pack File Requirements
+
+A pack whose `composition.yaml` is present is a **composition pack** (also called a *composite pack* — see `spec/COMPOSITION.md` for the full semantics). Composition packs reference claims in other packs via `↔` see_also relations rather than carrying their own evidence. The file requirements adjust as follows:
+
+| File | Standard pack | Composition pack |
+|------|---------------|------------------|
+| `PACK.yaml` | REQUIRED | REQUIRED |
+| `composition.yaml` | ABSENT | REQUIRED (defines the composition) |
+| `claims.md` | REQUIRED | REQUIRED — contents are intentionally minimal: claims describe the composition context itself (who, when, why, what changed), not the topics being composed (see COMPOSITION.md §3) |
+| `evidence.md` | RECOMMENDED — required in practice whenever any claim cites an evidence ID | OPTIONAL — may be omitted entirely |
+| Everything else (`history.md`, `entities.md`, `views/`, `definitions/`, `policies/`, `signatures.yaml`, `validation.yaml`) | unchanged | unchanged |
+
+A composition pack MUST NOT redefine the claims or evidence of a pack it references. Its `claims.md` contains only claims about the composition itself; the referenced packs remain the canonical source for their own content.
+
 ---
 
 ## 3. PACK.yaml — Manifest