v3.4.0

What's Changed

• TODO.md cleanup: drop SHIPPED rows, refresh stale refs, add Tier A/B/C/D backlog by @igerber in #447
• dCDH heterogeneity: per-path + global placebo predict_het R-parity + df threading by @igerber in #449
• Refresh METHODOLOGY_REVIEW.md to reflect current estimator catalog by @igerber in #448
• Add Goodman-Bacon (2021) paper review by @igerber in #451
• Regenerate clubsandwich_cr2_golden.json from authoritative R clubSandwich by @igerber in #450
• SpilloverDiD: ring-indicator spillover-aware DiD (Butts 2021) by @igerber in #446
• dCDH heterogeneity wrap-up: post-drop rank df + negative-baseline path test by @igerber in #452
• Wave 3 estimator observability: HonestDiD M=0 test, Wooldridge canonical-link warning, ARP vertex diagnostic by @igerber in #453
• BaconDecomposition methodology audit (Goodman-Bacon 2021) by @igerber in #454
• Wave 4 Tier A drain: EfficientDiD anticipation note, generate_ddd_panel_data, TROP data-setup helper by @igerber in #455
• BaconDecomposition R parity goldens by @igerber in #457
• SpilloverDiD: event_study=True per-event-time × ring decomposition (Wave C) by @igerber in #456
• DiD-absorb HC2/HC2-BM: auto-route to fixed_effects internally by @igerber in #458
• Lift MultiPeriodDiD-absorb HC2/HC2-BM gate via auto-route by @igerber in #459
• SpilloverDiD: Gardner GMM first-stage correction (Wave D) by @igerber in #462
• PreTrendsPower: Roth (2022) paper review + silent-failure guard by @igerber in #463
• Lift Gate 6: cluster-aware CR2 Bell-McCaffrey contrast DOF for MultiPeriodDiD avg_att by @igerber in #465
• Surface agent_workflow() + curated dir() for LLM discoverability (#460) by @igerber in #464
• Add agent-discoverability contract test (#461) by @igerber in #467
• PreTrendsPower implementation audit (Roth 2022 — PR-B) by @igerber in #466
• Release 3.4.0: SpilloverDiD (Butts 2021), Bacon R-parity goldens, agent-discoverability surface, PreTrendsPower R-parity audit by @igerber in #470

Full Changelog: v3.3.3...v3.4.0