feat: workout-suggester, weather-aware workouts from a local Gemma

Go + Templ + HTMX app that checks the weather (Open-Meteo, MET Norway
fallback), scores run/ride/walk with plain rules, and has a local
open-weight model (Gemma 4 E2B via any OpenAI-compatible server) write
the plan. Routes are loops from your door (BRouter) plus signposted
OpenStreetMap routes (Overpass), with GPX export.

internal/coach/prompt.go

@@ -0,0 +1,141 @@
+package coach
+
+import (
+	"fmt"
+	"strings"
+
+	"git.b0b.be/bdeb/workout-suggester/internal/routes"
+	"git.b0b.be/bdeb/workout-suggester/internal/weather"
+)
+
+// Plan is everything the model needs to know, gathered before it speaks.
+type Plan struct {
+	Place        string
+	At           routes.Point // exact; only used on this machine
+	Forecast     weather.Forecast
+	Request      Request
+	Assessment   Assessment
+	RoutesLoaded bool
+	Routes       []routes.Suggestion
+	Junction     *JunctionInfo
+	RoutesErr    string
+}
+
+// JunctionInfo is the nearest node-network junction to start from.
+type JunctionInfo struct {
+	Ref  string
+	Kind routes.Kind
+	Km   float64
+}
+
+// FirstQuestion is the hidden user turn that asks for the plan.
+const FirstQuestion = "What should I do right now?"
+
+// FollowUpHint is added to follow-up questions sent to the model.
+const FollowUpHint = "Answer in a few short lines, not the full plan format. Only change what I asked."
+
+const persona = `You are the coach inside "workout-suggester", an app that gets people off their screen and outside.
+The app has already checked the weather and scored each activity with fixed rules. Trust the FACTS below and never invent other numbers, temperatures, times or route names.
+Be warm, direct and brief: under 180 words, Markdown, no tables, no preamble.`
+
+const firstReplyFormat = `Answer the first question in exactly this shape:
+**<emoji> <the pick, e.g. "Go for a run">**: one sentence on why, citing the weather.
+**When:** now, or the better window from the FACTS if there is one.
+**The session:** 3–5 bullets: warm-up, a main set that matches the intensity and the minutes, cool-down. Hard = intervals or tempo; easy = conversational pace.
+**Route:** recommend the first listed route by its name and say how to use it (from the door, laps, out and back); mention its climb if it has one and fits the user's note. If no routes are listed, suggest an easy out-and-back from the door.
+**Wear:** one line for this weather.
+**Plan B:** one line.
+
+If the pick is an indoor workout, give a concrete HIIT, bodyweight or gym session for the minutes and intensity under **The session**, skip **Route** and **Wear**, and say under **When** whether it gets nicer outside later.`
+
+// SystemPrompt is the persona plus the facts and the answer format.
+func (p Plan) SystemPrompt() string {
+	return persona + "\n\n" + p.Facts() + "\n\n" + firstReplyFormat
+}
+
+// Facts is a compact, model-friendly summary of the plan.
+func (p Plan) Facts() string {
+	var b strings.Builder
+	f, a, r := p.Forecast, p.Assessment, p.Request
+	w := func(format string, args ...any) { fmt.Fprintf(&b, format+"\n", args...) }
+	desc, _ := weather.Describe(f.Now.Code)
+
+	w("FACTS")
+	where := p.Place
+	if where == "" {
+		where = "the user's location"
+	}
+	w("- Place: %s. Local time: %s. Sunset: %s.", where, f.Now.Time.Format("Mon 15:04"), f.Sunset.Format("15:04"))
+	gusts := fmt.Sprintf("gusts %.0f km/h", f.Now.Gusts)
+	if f.GustsEstimated {
+		gusts = fmt.Sprintf("gusts around %.0f km/h (estimated)", f.Now.Gusts)
+	}
+	chance := ""
+	if f.Now.PrecipProb >= 0 {
+		chance = fmt.Sprintf(", rain chance %d%%", f.Now.PrecipProb)
+	}
+	w("- Weather now: %.0f°C (feels like %.0f°C), %s, wind %.0f km/h from the %s, %s, rain %.1f mm%s.",
+		f.Now.Temp, f.Now.Feels, desc, f.Now.Wind, weather.Compass(f.Now.WindDirection), gusts, f.Now.Precip, chance)
+	w("- User wants: %s, %s intensity, %d minutes.", r.Activity.Noun(), r.Intensity, r.Minutes)
+	if r.Note != "" {
+		w("- User note: %q", r.Note)
+	}
+	w("- Scores for the next %d minutes (0-100, rules-based):", r.Minutes)
+	for _, s := range a.Scores {
+		why := "good conditions"
+		if len(s.Reasons) > 0 {
+			why = strings.Join(s.Reasons, "; ")
+		}
+		w("  - %s: %d (%s): %s", s.Activity.Noun(), s.Value, s.Verdict(), why)
+	}
+	w("- The app's pick: %s.", a.Pick.Noun())
+	if r.Activity != Any && r.Activity != a.Pick {
+		w("- The user asked for %s but the weather makes it a poor choice right now; explain kindly.", r.Activity.Noun())
+	}
+	if a.Later != nil {
+		w("- Better window: %s scores %d from %s.", a.Later.Activity.Noun(), a.Later.Score, a.Later.Start.Format("15:04"))
+	} else {
+		w("- Better window later today: none, now is as good as it gets.")
+	}
+	if a.TargetKm > 0 {
+		w("- Target: about %.1f km at %s.", a.TargetKm, a.Pace)
+	}
+	if a.Pick != Indoor {
+		switch {
+		case len(p.Routes) > 0:
+			w("- Routes, best fit first:")
+			for i, s := range p.Routes {
+				r := s.Route
+				if r.Generated {
+					extra := fmt.Sprintf(", %d m of climbing", r.AscentM)
+					if r.PavedPct >= 0 {
+						extra += fmt.Sprintf(", %d%% paved", r.PavedPct)
+					}
+					if r.IntoWind(f.Now.WindDirection) {
+						extra += ", heads out into the wind so the way home has a tailwind"
+					}
+					w("  %d. %q: a loop from the user's door, %.1f km%s.", i+1, r.Name, r.LengthKm, extra)
+					continue
+				}
+				loop := ""
+				if r.Loop {
+					loop = ", loop"
+				}
+				w("  %d. %q: signposted route, %.1f km%s, %.1f km from the user; suggested: %s (≈%.1f km).",
+					i+1, r.Name, r.LengthKm, loop, s.FromYouKm, s.Describe(), s.TotalKm)
+			}
+		case p.RoutesErr != "":
+			w("- Routes: the map service couldn't be reached, so no routes are listed.")
+		default:
+			w("- Routes: none found nearby.")
+		}
+		if j := p.Junction; j != nil {
+			kind := "walking"
+			if j.Kind == routes.Bike {
+				kind = "cycling"
+			}
+			w("- Nearest %s junction (knooppunt): number %s, %.1f km away.", kind, j.Ref, j.Km)
+		}
+	}
+	return strings.TrimRight(b.String(), "\n")
+}