IP-C1: Collaborative Ownership

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+NIP-C1
+======
+
+Collaborative Ownership
+-----------------------
+
+`draft` `optional`
+
+This NIP defines a mechanism for multiple pubkeys to collaboratively maintain addressable events while preserving backwards compatibility.
+
+## Motivation
+
+Certain applications require shared ownership where:
+
+1. **Attribution matters**: Each collaborator signs with their own key
+2. **Dynamic membership**: Owners can be added or removed
+3. **Backwards compatibility**: Non-supporting clients see normal events
+
+## Specification
+
+### Collaborative Pointer Event
+
+A new addressable event kind `39382` serves as a pointer to collaboratively-owned content:
+
+```jsonc
+{
+  "kind": 39382,
+  "pubkey": "<creator-pubkey>",
+  "tags": [
+    ["d", "<slug>"],
+    ["k", "<target-kind>"],
+    ["p", "<owner-1-pubkey>"],
+    ["p", "<owner-2-pubkey>"],
+    ["p", "<owner-3-pubkey>"]
+  ],
+  "content": "",
+  "created_at": 1234567890
+}
+```
+
+#### Tag Definitions
+
+| Tag | Required | Description |
+|-----|----------|-------------|
+| `d` | Yes | `<slug> |`
+| `k` | Yes | Target event kind |
+| `p` | Yes | Owner pubkeys (one or more) |
+
+### Resolution Algorithm
+
+To resolve the current state of collaboratively-owned content:
+
+1. Parse the `39382` pointer event to extract owners (`p` tags) and target kind (`k` tag)
+2. Extract the slug from the `d` tag (everything after the first `-`)
+3. Query: `{"kinds": [<target-kind>], "authors": [<all-owners>], "#d": ["<slug>"], "limit": 1}`
+
+### Back-Reference
+
+Target events MUST include an `a` tag pointing to the `39382` pointer:
+
+```jsonc
+{
+  "kind": 30023,
+  "tags": [
+    ["d", "my-article"],
+    ["a", "39382:<pointer-creator-pubkey>:30023-my-article"]
+  ]
+}
+```
+
+This allows clients to discover collaborative ownership from either direction: pointer → content or content → pointer.
+
+## Example
+
+### Pointer Event
+
+```jsonc
+{
+  "kind": 39382,
+  "pubkey": "alice-pubkey",
+  "tags": [
+    ["d", "collaborative-guide"],
+    ["k", "30023"],
+    ["p", "alice-pubkey"],
+    ["p", "bob-pubkey"],
+    ["p", "carol-pubkey"]
+  ],
+  "content": ""
+}
+```
+
+### Target Article (by any owner)
+
+```jsonc
+{
+  "kind": 30023,
+  "pubkey": "bob-pubkey",
+  "tags": [
+    ["d", "collaborative-guide"],
+    ["title", "A Collaborative Guide"],
+    ["a", "39382:alice-pubkey:30023-collaborative-guide"]
+  ],
+  "content": "..."
+}
+```
+
+### Client Resolution
+
+1. Client receives `naddr` for the `39382` pointer
+2. Parses owners: `[alice, bob, carol]`
+3. Queries: `{"kinds": [30023], "authors": ["alice", "bob", "carol"], "#d": ["collaborative-guide"], "limit": 1}`
+4. Returns most recent version regardless of which owner published it
+
diff --git a/README.md b/README.md
index c094d47..d9c889e 100644
--- a/README.md
+++ b/README.md
@@ -109,6 +109,7 @@ They exist to document what may be implemented by [Nostr](https://github.com/nos
 - [NIP-B7: Blossom](B7.md)
 - [NIP-BE: Nostr BLE Communications Protocol](BE.md)
 - [NIP-C0: Code Snippets](C0.md)
+- [NIP-C1: Collaborative Ownership](C1.md)
 - [NIP-C7: Chats](C7.md)
 - [NIP-EE: E2EE Messaging using MLS Protocol](EE.md) --- **unrecommended**: superseded by the [Marmot Protocol](https://github.com/marmot-protocol/marmot)
 
@@ -294,6 +295,7 @@ They exist to document what may be implemented by [Nostr](https://github.com/nos
 | `39000-9`     | Group metadata events           | [29](29.md)                            |
 | `39089`       | Starter packs                   | [51](51.md)                            |
 | `39092`       | Media starter packs             | [51](51.md)                            |
+| `39382`       | Collaborative Pointer           | [C1](C1.md)                            |
 | `39701`       | Web bookmarks                   | [B0](B0.md)                            |
 
 [NUD: Custom Feeds]: https://wikifreedia.xyz/cip-01/