Background job main session missing skills listing system-reminder (its subagents receive it)

Summary

A background job's main session does not receive the available-skills listing system-reminder, while subagents spawned from that same session do receive the full listing. Since the harness instructs the model to "only use skills listed in the user-invocable skills section — don't guess", the background-job main session effectively cannot discover or invoke any user/project skills.

Environment

• Claude Code v2.1.233
• macOS (darwin 25.5.0), zsh
• Session type: background job started from the agents (FleetView) interface, cwd inside a git repo
• Skills present: ~30 personal skills in ~/.claude/skills/ (each with valid SKILL.md frontmatter) + 1 project skill in <repo>/.claude/skills/

Observed

1. In the background job's main session, no system-reminder containing an available-skills listing ever appeared (verified across the full un-summarized conversation; deferred-tools listing and agent-types listing did appear).
2. A general-purpose subagent spawned from that same session, asked to report verbatim what it sees in its own context (tools forbidden), reported a complete skills listing with all ~48 entries (personal + project + built-in skills).
3. Consequence: the main session produced an HTML deliverable without loading the user's html-effectiveness skill (which encodes the user's binding page conventions and whose description matches the task), because it had no way to know the skill existed.

Expected

Background-job main sessions should receive the same available-skills listing as interactive sessions and subagents.

Repro sketch

1. Have personal skills in ~/.claude/skills/.
2. Start a session as a background job from the agents interface.
3. Ask the main session to list, without using tools, the skills listing visible in its context → none.
4. Have it spawn a subagent with the same question → full listing.