[ACT-15] Run a market-sizing sensitivity workshop

[EmersonBraun]

Goal

Run a sizing exercise that changes one assumption at a time: denominator, geography, period, or source. Structure assumptions, then review interpretation and sensitivity notes.

Evidence

• Human guide: docs/agents/research-market-sizing.md
• Agent test: registry/research-market-sizing/agent.test.ts

Acceptance criteria

• Assumptions and sources are explicit.
• At least one sensitivity change is documented.
• The output is labeled decision support, not a forecast.
• The workshop produces a reusable fixture or review note.

Human gate

A research or product strategy owner must approve the assumptions.