fix: tighten workspace_file_changed operation spec and fix doc escaping

Address PR review feedback:
- Constrain workspace_file_changed operation to only accept
  "create"|"update" (not "delete") using s/and, while keeping
  the correct :operation wire key name
- Remove backslash-escaped pipes in API.md table backtick content
  (GFM renders them literally)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: krukow

doc/reference/API.md

@@ -862,8 +862,8 @@ copilot/tool-events
 | `:copilot/session.compaction_start` | Context compaction started (infinite sessions) |
 | `:copilot/session.compaction_complete` | Context compaction completed (infinite sessions) |
 | `:copilot/session.mode_changed` | Session agent mode changed; data: `{:previous-mode "...", :new-mode "..."}` |
-| `:copilot/session.plan_changed` | Session plan created/updated/deleted; data: `{:operation "create"\|"update"\|"delete"}` |
-| `:copilot/session.workspace_file_changed` | Workspace file created or updated; data: `{:path "...", :operation "create"\|"update"}` |
+| `:copilot/session.plan_changed` | Session plan created/updated/deleted; data: `{:operation "create"/"update"/"delete"}` |
+| `:copilot/session.workspace_file_changed` | Workspace file created or updated; data: `{:path "...", :operation "create"/"update"}` |
 | `:copilot/session.task_complete` | Task completed by the session agent; data: `{:summary "..."}` (optional) |
 | `:copilot/skill.invoked` | Skill invocation triggered |
 | `:copilot/user.message` | User message added |

src/github/copilot_sdk/specs.clj

@@ -454,9 +454,10 @@
   (s/keys :req-un [::operation]))
 
 ;; Session workspace file changed event
-;; ::path already defined above; ::operation reused (superset covers both events)
+;; ::path already defined above; ::operation reused but constrained to create/update
 (s/def ::session.workspace_file_changed-data
-  (s/keys :req-un [::path ::operation]))
+  (s/and (s/keys :req-un [::path ::operation])
+         #(contains? #{"create" "update"} (:operation %))))
 
 ;; Session task complete event
 (s/def ::session.task_complete-data