feat(atlas): weight replay pacing on CI/CD stages by real job durations (#5)

TDD: Job.Seconds() + StageSeconds() derive real CI/CD dwell time from the
latest run's per-job created_at/updated_at (last job in pipeline order =
deploy/stage 07, everything before it = CI/stage 06).

Frontend: weightedSpineDist() redistributes the pixel-time-budget the
06/07 segments already had, splitting it by real CI:CD duration ratio
instead of raw pixel width. Falls back to the exact prior constant-speed
sweep when no run data is available (weights default to segment pixel
length) or when a job is skipped (0 duration) — no behavior change for
stages 00-05/08, which still have no live timing source (same gap as #5's
ledger item).

Verified: real duration values flow through /api/atlas.json (ci_duration_s:
18 observed against a real run), full page screenshot confirms no visual
regression.

internal/web/handler.go

@@ -55,6 +55,7 @@ func NewHandler() http.Handler {
 					a.Stages[i].Nodes = nodes
 				}
 			}
+			a.CIDurationS, a.CDDurationS = atlas.StageSeconds(*ld.run)
 		}
 		if ld.issues != nil {
 			for i := range a.Stages {

internal/web/static/cad-atlas.html

@@ -214,7 +214,7 @@
 // stage from the live cd.yml + substrate from the live cluster). These start
 // empty and are filled by init()'s fetch; on failure the page shows an error
 // banner rather than stale inline data.
-let SUBSTRATE=[], NS="", STAGES=[], TIMELINE=[];
+let SUBSTRATE=[], NS="", STAGES=[], TIMELINE=[], CI_DUR=0, CD_DUR=0;
 let MODE = localStorage.getItem('atlas-mode') || 'plain';   // 'plain' | 'technical'
 
 const track=document.getElementById('track');
@@ -330,14 +330,47 @@ function build(){
   }
   spineLen=spinePath.getTotalLength();loopLen=loopPath.getTotalLength();
 }
+// weightedSpineDist maps f (0..1 time-progress across the spine) to an arc-length
+// distance. Default weight per stage-to-stage segment is its own pixel length —
+// reduces to the old constant-pixel-speed sweep. When a real run's CI/CD durations
+// are known, the pixel-time-budget already held by the 06(CI)/07(CD) segments is
+// re-split by their real relative duration instead of by raw pixel width — so the
+// reel visits stage 06 vs 07 at speeds proportional to how long they actually took.
+function weightedSpineDist(f){
+  const n=cs.length-1;
+  if(n<=0)return 0;
+  const segLens=[];for(let i=0;i<n;i++)segLens.push(cs[i+1]-cs[i]);
+  const weights=segLens.slice();
+  if(CI_DUR>0&&CD_DUR>0&&n>=7){
+    const budget=weights[5]+weights[6], tot=CI_DUR+CD_DUR;
+    weights[5]=budget*CI_DUR/tot; weights[6]=budget*CD_DUR/tot;
+  }
+  const totalW=weights.reduce((a,b)=>a+b,0);
+  const target=f*totalW;
+  let acc=0;
+  for(let i=0;i<n;i++){
+    if(target<=acc+weights[i]||i===n-1){
+      const local=weights[i]>0?(target-acc)/weights[i]:0;
+      const segStart=cs[i]-cs[0];
+      return Math.min(spineLen,Math.max(0,segStart+segLens[i]*Math.min(1,Math.max(0,local))));
+    }
+    acc+=weights[i];
+  }
+  return spineLen;
+}
 function run(ts){
   if(mobile)return;
   if(!t0)t0=ts;
   const dur=slow?16000:7000;
   const p=Math.min((ts-t0)/dur,1);
-  const total=spineLen+loopLen, dist=total*p;
-  let pt,onLoop=dist>spineLen;
-  pt=onLoop?loopPath.getPointAtLength(dist-spineLen):spinePath.getPointAtLength(dist);
+  const spineFrac=spineLen/(spineLen+loopLen);
+  let dist,onLoop;
+  if(p<spineFrac){
+    dist=weightedSpineDist(p/spineFrac); onLoop=false;
+  }else{
+    dist=spineLen+loopLen*((p-spineFrac)/(1-spineFrac)); onLoop=true;
+  }
+  let pt=onLoop?loopPath.getPointAtLength(dist-spineLen):spinePath.getPointAtLength(dist);
   pulse.style.left=pt.x+'px';pulse.style.top=pt.y+'px';
   pulse.style.background=onLoop?'var(--violet)':'var(--amber)';
   pulse.style.boxShadow=onLoop?'0 0 15px 4px rgba(155,140,255,.75)':'0 0 15px 4px rgba(245,185,66,.75)';
@@ -370,6 +403,8 @@ async function init(){
     if(typeof data.ns==='string') NS=data.ns;
     if(Array.isArray(data.stages)) STAGES=data.stages;
     if(Array.isArray(data.timeline)) TIMELINE=data.timeline;
+    if(typeof data.ci_duration_s==='number') CI_DUR=data.ci_duration_s;
+    if(typeof data.cd_duration_s==='number') CD_DUR=data.cd_duration_s;
     if(data.version) document.getElementById('ver').textContent=data.version;
   }catch(e){
     console.error('atlas: failed to load /api/atlas.json —',e);