Diagnose a plant problem from symptoms

Something is wrong with a plant and the internet says it is either too much or too little water.

Diagnose my plant from the symptoms below. Work like a clinician, not a search engine.

1. **Questions first.** Ask me up to six questions whose answers would most narrow this down: where the damage started, whether it spread, what the roots look like, watering habits, light, recent changes, undersides of leaves. Ask them all in one go.
2. **Differential.** Once I answer, give three or four possible causes ranked by likelihood, and for each, the distinguishing sign that confirms or rules it out.
3. **The check.** One thing to physically do or look at right now that separates the top two candidates.
4. **Treatment** for the most likely cause, as steps, with what improvement to expect and by when.
5. **What is already lost.** Which damaged parts will never recover and should be removed, versus which will grow out.

Do not guess a cause from a vague description. If the symptoms are genuinely ambiguous, say so and tell me what to photograph or inspect.

Plant:
Symptoms and when they started:
Conditions:

Diagnosis and rescue. Working out what is wrong with a plant, what is eating it, and whether it is worth saving at all.