docs: document named agent base prompts and harness-specific model IDs

[hongyi-chen]

What

Three fixes to reference/cli/index.mdx:

1. Documents oz agent create --prompt and oz agent update --prompt / --remove-prompt.
2. Documents that --model takes harness-specific model IDs when paired with --harness claude
   or --harness codex, with an example.
3. Removes a duplicated block: --harness, --claude-auth-secret, and --codex-auth-secret were
   each listed twice in the run-cloud flag list with conflicting wording.

Why

Items 1 and 2 were flagged by the missing_docs changelog cross-check (2026.07.31: "The oz CLI
can now set a named agent's prompt when creating or updating agents" and "The oz CLI now accepts
harness-specific model IDs with --harness claude and --harness codex"). Item 3 was spotted while
verifying those flags against the CLI source.

Source of truth

• crates/warp_cli/src/agent.rs — AgentCreateArgs::prompt ("Base prompt for runs of this agent")
  and AgentUpdateArgs::prompt / remove_prompt.
• crates/warp_cli/src/model.rs — ModelArgs, which documents oz model list for the default
  harness and pass-through of harness-specific values for third-party harnesses.

Deferred findings from this run

Nothing from the audit was silently dropped. The full deferral list lives in the companion
bookkeeping PR (docs/missing-docs-audit-bookkeeping); in summary:

• 15 warp-server public API routes missing from the OpenAPI spec — routed to the
  sync-openapi-spec skill rather than hand-written, per the skill's public/private guardrail.
• 32 terminology/staleness findings — owned by the style_lint skill.
• 1 new server-side agent tool (report_external_reference) — reached only through the hidden
  oz harness-support CLI, so no public surface to document yet.

---

Conversation: https://staging.warp.dev/conversation/c45bb2ea-d33b-4723-8249-478547f81a47
Run: https://oz.staging.warp.dev/runs/019fc891-7c04-779b-b006-328169d8a0d7

This PR was generated with Oz.

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Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview	Aug 3, 2026 5:21pm

[hongyi-chen]

Closing as a duplicate: #440 already documents harness-specific --model IDs (and removes the same duplicated --harness/auth-secret flag block), and #387 already documents the named-agent --prompt / --remove-prompt flags. Between them they fully cover this PR.

Found while running the missing_docs drift-watch skill, which flagged both items from the 2026.07.31 changelog. I didn't check for existing open PRs before drafting — my mistake.

Both #440 and #387 touch reference/cli/index.mdx, so they'll need sequencing against each other, but each is on a current path and neither is affected by the agent-platform/ → agents/ rename.