tb-v1: model total_bases as a compound outcome (challenger)

Current ladder (proj_p_over_line) and champion p_win are BYTE-IDENTICAL.
tb-v1 writes alongside them, on total_bases props only.

STEP 0 -- components confirmed on real data, not assumed. statsapi has no
singles field, but hits - doubles - triples - homeRuns reproduces stored
totalBases EXACTLY on a real 10-game log. So the decomposition is exact,
not an approximation.

THE MODEL. Each component gets its own per-game Poisson rate; TB is their
weighted sum, and the PMF is built by exact convolution rather than
simulated (TB support is small). It inherits the SAME combined multiplier
proj-v1.1 computes, so the two models differ only in STRUCTURE.

Why this is the fix: with identical mean TB of 1.0, a pure-HR hitter and a
pure-singles hitter get P(TB>=4) of 0.221 vs 0.019 -- a 12x difference an NB
on TB alone cannot express, because it treats one home run as four events.
A test asserts that separation, and asserts P(TB>=4) for a pure-HR hitter
equals P(at least one HR) exactly.

INDEPENDENCE IS AN APPROXIMATION AND IS LABELLED AS ONE: a plate appearance
that becomes a double cannot also become a single, so the components are
weakly negatively correlated and independent Poissons slightly overstate
the tail. Closer to the truth than what it replaces; not a solved problem.

HONEST-ABSENT throughout: fewer than 3 usable games, or no derivable
component, returns null and the prop keeps the current ladder value. An
inconsistent row (hits < extra-base hits) is SKIPPED rather than clamped to
zero -- clamping would invent a plausible line out of a broken one.

I HIT THE Number(null)===0 TRAP IN MY OWN CODE and a test caught it: a null
rate passed a naive finite check and was treated as a measured zero, which
is the difference between "this player never triples" and "we do not know
his triple rate". Both tbPmf and tbMean now reject null/''/boolean strictly.

Holdout committed: TB ROWS ONLY (49 of 437 settled -- averaging into other
stats would hide the effect) and DIRECTION-ALIGNED, since the unaligned
comparison is the artifact that accounted for 41% of the ladder's apparent
loss. If tb-v1 does NOT improve, the family-mismatch hypothesis is wrong
and the mean/similarity branch reopens -- recorded in the query header.

Migration applied: proj_tb_p_over + proj_tb_meta, NULL-meaningful.

Gates: 4,104 tests / 329 suites green; next build exit 0.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QJs13VsyiSKYQP6rj3NNmc

src/services/ledgerService.js

@@ -293,6 +293,11 @@ function rowsFromSnapshot(sport, grades, oddsProps, nowIso) {
       proj_distribution: g.proj_distribution || null,
       proj_ladder: g.proj_ladder || null,
       proj_factors: g.proj_factors || null,
+      // tb-v1 CHALLENGER — total_bases as a compound outcome. Written alongside
+      // proj_p_over_line, never in place of it. NULL on non-TB props and when
+      // the components are underivable; never a fabricated 0.
+      proj_tb_p_over: numOrNull(g.proj_tb_p_over),
+      proj_tb_meta: g.proj_tb_meta || null,
       // Session 75 — the ENVIRONMENT that drove this projection. The FORECAST,
       // not the actual: this is what we knew when we projected, and it is what
       // the instrument measures. The actual lands in game_context and is never