docs(session-flow): recheck and point the orchestrate model and cost claims #7991

Refs: #6916

Agent Brief

Type: Task
Summary: Re-verify the five orchestrate findings from the #6916 pilot and point the ones that still lack an upstream pointer.

Current behavior:
The pilot flagged the orchestrate skill's model-resolution fact, two cost judgments (delegate bulk work; tune effort), the withheld from non-fork workers claim and the workflow size bands. Since then the skill points at sub-agents#choose-a-model and workflows#set-a-size-guideline, and its sources record points at sub-agents#available-tools, so some findings may be resolved; no pointer to the optimizing-for-cost-and-intelligence page appears in the skill.

Desired behavior:
Each of the five claims either carries a pointer (https://platform.claude.com/docs/en/about-claude/models/optimizing-for-cost-and-intelligence sections for the two judgments; the sub-agents sections for the others) with an as-of date and recheck trigger, or the PR body says it already does and where. Size bands match the workflows section they cite or are replaced by the pointer. No price or cost figure is added.

Key interfaces:

• The orchestrate skill's claims and its sources record.

Acceptance criteria:

• The PR body lists all five findings, each marked fixed or already pointed, with the line it points from.
• check-skill.sh passes for the orchestrate skill.
• A session-flow changelog fragment is added and scripts/check-changelog-fragments.sh passes.

Out of scope:

• Rewording the skill beyond the pointed claims.
• The README haiku pin, already gone on main.

This was generated by AI during backlog shaping. Split from #6916; the owner approved filing it in an attended backlog-shaping session on 2026-10-18.