fix: update proxy and snapshots for eager skill injection

The runtime now eagerly injects skill content into <agent_instructions>
in the user message instead of using a skill tool call. Update the
replay proxy to strip <agent_instructions> during normalization, and
simplify the snapshot for agent-with-skills to match the new flow.

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

Author: MackinnonBuck

test/harness/replayingCapiProxy.ts

@@ -805,6 +805,8 @@ function normalizeUserMessage(content: string): string {
   return content
     .replace(/<current_datetime>.*?<\/current_datetime>/g, "")
     .replace(/<reminder>[\s\S]*?<\/reminder>/g, "")
+    .replace(/<agent_instructions>[\s\S]*?<\/agent_instructions>/g, "")
+    .replace(/<agent_instructions>[\s\S]*?<\/agent_instructions>/g, "")
     .replace(
       /Please create a detailed summary of the conversation so far\. The history is being compacted[\s\S]*/,
       "${compaction_prompt}",

test/snapshots/skills/should_allow_agent_with_skills_to_invoke_skill.yaml

@@ -6,39 +6,5 @@ conversations:
         content: ${system}
       - role: user
         content: Say hello briefly using the test skill.
-      - role: assistant
-        tool_calls:
-          - id: toolcall_0
-            type: function
-            function:
-              name: skill
-              arguments: '{"skill":"test-skill"}'
-      - role: tool
-        tool_call_id: toolcall_0
-        content: Skill "test-skill" loaded successfully. Follow the instructions in the skill context.
-      - role: user
-        content: >-
-          <skill-context name="test-skill">
-
-          Base directory for this skill: ${workdir}/.test_skills/test-skill
-
-
-          ---
-
-          name: test-skill
-
-          description: A test skill that adds a marker to responses
-
-          ---
-
-
-          # Test Skill Instructions
-
-
-          IMPORTANT: You MUST include the exact text "PINEAPPLE_COCONUT_42" somewhere in EVERY response you give. This
-          is a mandatory requirement. Include it naturally in your response.
-
-
-          </skill-context>
       - role: assistant
         content: Hello! PINEAPPLE_COCONUT_42 - I'm ready to help you with your tasks today.