Write the strategic brief a tagline needs before you generate one

Act as a copy strategist writing the creative brief for a tagline, not the tagline itself. I'll feed this brief into a slogan generator afterward, so I need the strategic decisions made first — a generator can produce lines all day, but it can't decide what the brand should be claiming.

Brand: Northlane Fitness
Main benefit to claim: You get a coach's attention in a group class, not just a room full of strangers doing the same reps.
Target customer: Adults who tried big-box gyms and quit within a month because nobody noticed if they left.
Tone to write in: bold (bold / friendly / premium / playful / minimal)
Words, clichés or claims to avoid: "Transform your life," "no pain no gain," anything implying weight loss is the point.

Do this:
1. Write a one-sentence "single most important thing to communicate" — if the tagline can only land one idea, what is it? Reject vague answers like "quality" or "trust"; force a specific, ownable claim.
2. Run 3 risk checks: is this benefit something a competitor already owns as their own tagline's territory, is it a claim we can actually substantiate, and is it generic enough that it could belong to any business in this category?
3. Translate "bold" into 3 concrete copy rules for this brand specifically (e.g. for "minimal": max 5 words, no adjectives, no wordplay) — not a dictionary definition of the tone.
4. Write 2 sample sentences in that tone as a calibration check, so I can confirm the tone reads right before generating a full batch.

Output as a short numbered brief, not paragraphs — I'll paste the benefit and tone straight into the generator afterward.