STARTER_GUIDE.md step 3 claims dedup works, but dedup is M5 scope (not shipped) #165

Context

Found during PR #63 review on 3 Nov 2026.

docs/STARTER_GUIDE.md (added by PR #63) includes a "Your first change: a guided walkthrough" section with 5 steps. Step 3 is actively wrong:

3. Re-upload the same file. Confirm duplicate detection kicks in (content-hash based, not filename based).

The current app does not have content-hash dedup. That capability is scoped to ART Milestone 5 (#109: "dedup and naming — per-tenant file dedup, record dedup, versioned datasets, BR-28..31"), which has not been started.

A new reader following step 3 will see no "duplicate detected" response. They'll either think they did something wrong, or that the walkthrough is wrong.

Options

(a) Remove step 3 entirely until M5 ships. The remaining 4 steps still exercise both modes and the test suite — still a useful ten-minute walkthrough.
(b) Mark step 3 as "when M5 ships". Leaves readers knowing dedup is coming, but doesn't invite them to try something that won't work.
(c) Both — remove it from the main numbered sequence, add a short "coming in M5" note in the surrounding prose.

Done when

• Decision taken on (a)/(b)/(c)
• docs/STARTER_GUIDE.md edited accordingly, one small PR
• When M5 ships, the step comes back (if removed) or the "coming" note goes away

Related

• PR docs: starter guide #63 adds the file
• ART M5: dedup and naming — per-tenant file dedup, record dedup, versioned datasets (BR-28..31) #109 (M5): where dedup will actually be implemented
• Live pointers to superseded docs/API_INTEGRATION.md need to be resolved #164: separate issue about STARTER_GUIDE's live pointer to superseded API_INTEGRATION.md