fix(atlas): allow boulder continuation for Sisyphus sessions

When boulderState.agent is not explicitly set (defaults to 'atlas'),
allow continuation for sessions where the last agent is 'sisyphus'.
This fixes the issue where boulder continuation was skipped when
Sisyphus took over the conversation after boulder creation.

src/hooks/atlas/event-handler.ts

@@ -89,13 +89,20 @@ export function createAtlasEventHandler(input: {
         return
       }
 
-      const requiredAgent = (boulderState.agent ?? "atlas").toLowerCase()
       const lastAgent = getLastAgentFromSession(sessionID)
-      if (!lastAgent || lastAgent !== requiredAgent) {
+      const requiredAgent = (boulderState.agent ?? "atlas").toLowerCase()
+      const lastAgentMatchesRequired = lastAgent === requiredAgent
+      const boulderAgentWasNotExplicitlySet = boulderState.agent === undefined
+      const boulderAgentDefaultsToAtlas = requiredAgent === "atlas"
+      const lastAgentIsSisyphus = lastAgent === "sisyphus"
+      const allowSisyphusWhenDefaultAtlas = boulderAgentWasNotExplicitlySet && boulderAgentDefaultsToAtlas && lastAgentIsSisyphus
+      const agentMatches = lastAgentMatchesRequired || allowSisyphusWhenDefaultAtlas
+      if (!agentMatches) {
         log(`[${HOOK_NAME}] Skipped: last agent does not match boulder agent`, {
           sessionID,
           lastAgent: lastAgent ?? "unknown",
           requiredAgent,
+          boulderAgentExplicitlySet: boulderState.agent !== undefined,
         })
         return
       }