chore: publish from staged

plugins/phoenix/skills/phoenix-tracing/references/span-chain.md

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+# CHAIN Spans
+
+## Purpose
+
+CHAIN spans represent orchestration layers in your application (LangChain chains, custom workflows, application entry points). Often used as root spans.
+
+## Required Attributes
+
+| Attribute                 | Type   | Description     | Required |
+| ------------------------- | ------ | --------------- | -------- |
+| `openinference.span.kind` | String | Must be "CHAIN" | Yes      |
+
+## Common Attributes
+
+CHAIN spans typically use [Universal Attributes](fundamentals-universal-attributes.md):
+
+- `input.value` - Input to the chain (user query, request payload)
+- `output.value` - Output from the chain (final response)
+- `input.mime_type` / `output.mime_type` - Format indicators
+
+## Example: Root Chain
+
+```json
+{
+  "openinference.span.kind": "CHAIN",
+  "input.value": "{\"question\": \"What is the capital of France?\"}",
+  "input.mime_type": "application/json",
+  "output.value": "{\"answer\": \"The capital of France is Paris.\", \"sources\": [\"doc_123\"]}",
+  "output.mime_type": "application/json",
+  "session.id": "session_abc123",
+  "user.id": "user_xyz789"
+}
+```
+
+## Example: Nested Sub-Chain
+
+```json
+{
+  "openinference.span.kind": "CHAIN",
+  "input.value": "Summarize this document: ...",
+  "output.value": "This document discusses..."
+}
+```