refactor(tui): extract s4 union (attachments_mixin + billing_wire_mixin) from server.py

[andrexibiza]

Godfile kill — tui_gateway/server.py shard s4

Extracts the attachments mixin (w1b) and billing-wire mixin (w1a) from tui_gateway/server.py into tui_gateway/attachments_mixin.py and tui_gateway/billing_wire_mixin.py (5x2x3 blind-witness extraction, waves 1-3 verified). Verbatim method bodies; module-level test constants stay; regression tests shipped.

Line math: 688 added / 377 deleted in server.py (moved into the two new mixin modules).

Related #78791 #78792 #77376 #77746 #77748 #77751 #77752 #77756 #77759 #79066 #79067 #79068 #79069 #79070 #78689 #78690 #78691 #78692 #78693 #78694 #78695 #78696 #78697 #78698 #78699 #78700 #78701 #78702 #78703 #78704 #78705 #78706 #78707 #78708 #78709 #78710 #78711 #78712 #78713 #78714 #78715 #78716 #78717 #78718 #78719 #78720 #78721 #78722 #78723 #78724 #78725 #78726 #78727 #78728 #78729 #78730 #78731 #78732 #78733 #78734 #78735 #78736 #78737 #78738 #78739 #78740 #78741 #78742 #78743 #78744 #78745 #78746 #78747 #78748 #78749 #78750 #78751 #78752 #78753 #78754 #78755 #78756 #78757 #78758 #78759 #78760 #78761 #78762 #78763 #78764 #78765 #78766 #78767 #78768 #78769 #78770 #78771 #78772 #78773 #78774 #78775 #78776 #78777 #78778 #78779 #78780 #78781 #78782 #78783 #78784 #78785 #78786 #78787 #78788 #78789 #78790

[spfcraze]

This was generated by AI during triage.

Summary:
The title says this PR extracts workspace/worker mixins from kanban_db.py (shard s4), but the diff contains no change to hermes_cli/kanban_db.py — the actual content is the tui_gateway/server.py shard s4 extraction (attachments_mixin + billing_wire_mixin), as the body and commit message already state.

Problems:

• The PR diff adds tui_gateway/attachments_mixin.py and tui_gateway/billing_wire_mixin.py and edits tui_gateway/server.py and tests/tui_gateway/test_server_s4_attachments_extraction.py; "kanban_db" appears nowhere in it, and hermes_cli/kanban_db.py (which exists at origin/main with its own test suite) is untouched.
• The commit bac66d9 is titled "refactor(tui): extract s4 union (attachments_mixin w1b + billing_wire_mixin w1a) from server.py" — matching the body and the diff, not the PR title.
• The body's "Line math: 2 added / 0 deleted in run.py" names run.py, which is not among the files this PR changes.

Solution:
As a title matching the diff: "refactor(tui): extract s4 union (attachments_mixin + billing_wire_mixin) from server.py" — the message of commit bac66d9, which is what this PR actually contains.

---

Checked against bac66d9 — the tip of gfg/tui-extract-s4-w1b when this was written — and 9ea0197, main at the same moment.

[andrexibiza]

Good catch — the title and body misdescribed the diff. Corrected:

• Title → refactor(tui): extract s4 union (attachments_mixin + billing_wire_mixin) from server.py (matches commit bac66d9 and the actual changed files).
• Body → now names tui_gateway/server.py (not run.py) and the two extracted mixins (attachments_mixin.py + billing_wire_mixin.py), with the correct line math: 688 added / 377 deleted in server.py.

No code change needed — the extraction itself was already the server.py s4 shard; the metadata was stale from the campaign template. Validation on this branch: tests/tui_gateway/test_server_s4_attachments_extraction.py passes (via scripts/run_tests.sh), git diff --check clean.