[upstream-sync] Port session.handoff :host field from copilot-sdk v0.2.0 (upstream PR #900)

CHANGELOG.md

@@ -2,6 +2,8 @@
 All notable changes to this project will be documented in this file. This change log follows the conventions of [keepachangelog.com](http://keepachangelog.com/).
 
 ## [Unreleased]
+### Added (v0.2.0 sync)
+- **`:host` field on `session.handoff` events** — `session.handoff` event data now includes an optional `:host` field with the GitHub host URL for the source session (e.g., `"https://github.com"` or `"https://tenant.ghe.com"`). New `::session.handoff-data` spec documents the shape: `{:remote-session-id "..." :host "..."}` (both optional) (upstream PR #900).
 
 ## [0.2.0.0] - 2026-03-23
 ### Added (v0.2.0 sync)

doc/reference/API.md

@@ -993,7 +993,7 @@ Convert an unqualified event keyword to a namespace-qualified `:copilot/` keywor
 | `:copilot/session.idle` | Session finished processing |
 | `:copilot/session.info` | Informational session update |
 | `:copilot/session.model_change` | Session model changed |
-| `:copilot/session.handoff` | Session handed off to another agent |
+| `:copilot/session.handoff` | Session handed off to another agent; data: `{:remote-session-id "..." :host "https://github.com"}` (both optional) |
 | `:copilot/session.usage_info` | Token usage information |
 | `:copilot/session.context_changed` | Session context (cwd, repo, branch) changed |
 | `:copilot/session.title_changed` | Session title updated |

src/github/copilot_sdk/specs.clj

@@ -540,6 +540,11 @@
 
 (s/def ::session.idle-data map?)
 
+(s/def ::remote-session-id string?)
+
+(s/def ::session.handoff-data
+  (s/keys :opt-un [::remote-session-id ::host]))
+
 (s/def ::agent-mode #{:interactive :plan :autopilot :shell})
 (s/def ::interaction-id string?)