Codex DM solo openings should not load unconfigured companions

[100yenadmin]

Summary

A current-head built-app Codex-DM proof on 8031445 minted a playable app session, but the opening turn attempted to load Shadowheart as a companion in a solo launch. The safety layer cancelled the tool call twice before the model recovered.

Evidence

• Run: codex-app-campaignhint-20260601T033155
• Minted run: play-20260531203202
• Built app SHA: 8031445
• Provider trace: play-state/play-20260531203202/codex-provider/codex-dm.stdout.jsonl
• Cancelled tool calls: load_canon_character(... kind="companion", add_to_party=true) for Shadowheart.

User Impact

The first turn still becomes playable, but cancelled tool calls add latency/noise to a fresh-player opening and can make readiness feel stalled.

Acceptance Criteria

• Codex DM opening prompts explicitly say solo native/provider sessions must not add companions unless CLAWDND_PLAY_COMPANIONS names them.
• The DM can still stage canon NPCs in narration without mutating party companion state.
• A focused wrapper test locks the instruction into the prompt surface.

[100yenadmin]

Addressed on PR #475 at commit 500c379. The final exact-head run codex-app-final-20260601T033714 did not attempt load_canon_character(... kind=\"companion\"); Shadowheart was staged as an NPC in narration only. Remaining safety-noise found in that run is tracked separately in #479. Leaving open until #475 merges.

[100yenadmin]

Closed after PR #475 merged. The Codex DM opening no longer loads unconfigured solo companions; the remaining setup/social cancellation noise is tracked separately in #479.