[HughRunyan]

User story

As an advanced DST user, I want a diversion share to mean what actually happens, so that "compost 10% of our waste" composts 10%, and every number I type or read refers to the same thing.

What changes

advanced_dst_city._diverted_masses stops applying reject and yield rates. Before:

• composting lost 10–19% of what it was sent, by material, in two stacked cuts (non_compostable_not_targeted, then unprocessable);
• recycling kept only each material's yield;
• combustion lost 10%.

All of that went back to the landfills. So a city told to compost 10% composted about 8.7%, and the landfills received the rest on top of their stated shares. Anaerobic digestion already kept everything.

Now every pathway keeps everything it is sent. _diverted_masses returns one DivsDF. The separate gross figure was there to catch over-diversion before rejects. It is now the same thing, so over_diversion measures the residual directly.

Effect. A city of 1 Mt a year with no gas capture, in 2040:

Diversion	Landfilled before	Landfilled after	Methane
compost 10%	913,039 t	900,000 t	−2.3%
compost 10% + recycling 10%	827,326 t	800,000 t	−4.8%
compost 30% + recycling 15%	610,547 t	550,000 t	−16.7%

Unchanged:

• The city DST, the site tool, the cities table and Climate TRACE all keep City's rates. city_params.py is untouched.
• A burning facility (combusts) in the advanced DST still buries combustion_reject_rate. That is a separate rate, which main already set to 0 in Waste sent to incineration stops producing methane #100; it arrives here with the next merge of main into am-waste-flow. Zeroing it on this branch now would make an incinerator's Sites-tab intake read 0 t, because the mass flow reports what a site buries rather than what it takes in.

Why

Hugh's call, 2026-10-28: rejects are minor, and they made every share a user states mean something smaller than what they typed. Removing them also clears two earlier problems:

• In the 2026-08-31 reject audit, composting's rejects were essentially the whole reason digestion looked 29% cleaner than composting.
• A site loaded with its WasteMAP record ended up 5–6% above that record (RMI/WasteMAP#917).

Acceptance criteria

• A stated compost, recycling or digestion share is exactly the mass diverted.
• Landfilled plus diverted still equals what is generated, less prevention.
• The city DST's City paths are unchanged.
• The changelog states the effect.

Testing

• pytest -m "not integration": 659 passed.
• test_diverted_is_the_whole_requested_share replaces the test that required rejects. test_recycling_and_digestion_keep_everything_they_are_sent covers the other pathways.
• WasteMAP's side is RMI/WasteMAP#921, which pins this branch; its ADST, incineration and decisions tests pass against it.

Definition of Done

Acceptance criteria met · tests and checks pass · changelog updated · reviewed and merged (merge commit).

🤖 Generated with Claude Code

[Copilot]

🟡 Changes recommended

The mass-flow tests omit combustion diversion, leaving a regression to the old 10% combustion loss untested.

1 open issue

• Add mass-flow coverage for combustion diversion · New

What changed in this PR

This PR makes city-level advanced DST diversion shares equal the mass actually diverted, without changing the legacy City paths or facility reject handling.

Changes:

• Removes pathway reject and yield reductions and simplifies residual validation.
• Updates mass-flow tests and routing helpers for the single diversion result.
• Documents the resulting landfill and methane reductions.

File	Description
tests/​test_adst_city_mass_flow.py	Checks full requested diversion shares and mass balance.
tests/​test_adst_city_diversion_routing.py	Adapts the helper to the single DivsDF return value.
SWEET_python/​advanced_dst_city.py	Removes pathway losses and simplifies residual calculations.
changelog/​2026-10.md	Records model-output changes and unchanged behavior.

_{Review effort: Balanced}