TPC TimeSeries: use the outer TRD state for the TRD-TPC residuals

- The TRD side of deltaTRDTPC, of the matching chi2 and of trdIn is now
  the outer state of the ITS-TPC-TRD track (TrackTRD::getOuterParam():
  outward refit through ITS, TPC and TRD, at the outermost TRD layer),
  propagated inward to the 275 cm plane, as RecoContainer does. The base
  state used before is the inward refit, which ends at the innermost ITS
  cluster, i.e. the combined track at the vertex.
- Comments corrected: TrackTRD has two parameter sets; the outward refit
  includes the TPC clusters, so TRD - TPC is not independent; full list of
  meaningful getters of deltaTRDTPC.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YYeB7SW1TM7vU8qhVHiG61

Author: miranov25

Detectors/TPC/workflow/src/TPCTimeSeriesSpec.cxx

@@ -399,7 +399,9 @@ class TPCTimeSeries : public Task
             trdData.trackletIndices[iLay] = trkltId;
           }
         }
-        trdData.trdTrackParCov = o2::track::TrackParCov(trdTrack); // TrackTRD base state, not validated as the outer/entrance state (open Phase 0.4 finding)
+        // outer state of the ITS-TPC-TRD track: outward refit through ITS, TPC and TRD, at the outermost TRD layer (as in
+        // RecoContainer::getTrackParamOut). The base state of TrackTRD is the inward refit, which ends at the innermost ITS cluster.
+        trdData.trdTrackParCov = trdTrack.getOuterParam();
         trdData.hasTRDTrackPar = true;
         tpcToTRDMap[refTPC] = trdData;
       }
@@ -1486,9 +1488,9 @@ class TPCTimeSeries : public Task
 
         // TPC-out / TRD-in states on a common local X plane, computed for every written entry (Architect decision 2026-10-28:
         // residuals always stored; only the full TrackPar objects depend on --store-full-trackpar).
-        // Open Phase 0.4 findings, deferred: the target is local X = kTPCTRDMiddle in the frame rotated to the track
-        // position angle (lab radius = sqrt(X^2 + Y^2), not exactly 275 cm), and the TRD starting state is the TrackTRD
-        // base state (TrackTRD carries a single parameter set), not validated as the outer/entrance state.
+        // Open Phase 0.4 finding, deferred: the target is local X = kTPCTRDMiddle in the frame rotated to the track position
+        // angle (lab radius = sqrt(X^2 + Y^2), not exactly 275 cm). The TRD side is the outer state of the ITS-TPC-TRD track,
+        // propagated inward to the plane; its outward refit includes the TPC clusters, so TRD - TPC is not independent.
         static constexpr float kTPCTRDMiddle = 275.f;            // cm, common local X plane between TPC outer wall and TRD layer 0
         static constexpr uint32_t kDeltaTRDTPCMask = 0xFFFFE000; // keep 10 mantissa bits: float16-like relative precision ~1e-3
         o2::track::TrackParCov tpcOutCov;                        // local temporary with covariance (needed for chi2); persisted as TrackPar
@@ -1499,7 +1501,9 @@ class TPCTimeSeries : public Task
         float chi2ZTPCTRD = -1.f;
         // deltaTRDTPC: TrackPar used as a residual container. mX and mAlpha = the common plane and frame (full precision,
         // copied from the propagated TPC state); mP[0..4] = TRD - TPC of Y, Z, Snp, Tgl, Q2Pt, truncated to 10 mantissa bits.
-        // Only getX(), getAlpha() and getParam(i) are meaningful (getPt(), getPhi(), ... are not). Default (X = 0) if trdInOK != 0.
+        // Meaningful: getX(), getAlpha(), getParam(i), getY(), getZ(), getSnp(), getTgl(), getQ2Pt(); not meaningful: derived
+        // getters (getPt(), getP(), getPhi(), getEta(), getCurvature(), ...). Charge, PID and user field are those of the TPC
+        // track. Default object (X = 0, parameters 0) if trdInOK != 0: select with trdInOK == 0.
         o2::track::TrackPar deltaTRDTPC;
         // D1: TPC outer → kTPCTRDMiddle
         tpcOutCov = o2::track::TrackParCov(tracksTPC[iTrk].getParamOut());