T9: Complex logic: calculation, relevance, constraint #9

Importance: Must have · Size: L · Depends on: T1, T8

Why. The logic columns are where clinical intent actually lives. The design doc places them in
Phase 2, but they are marked must-have: without them the tool can only edit wording, and a
program cannot own its own decision support.

Scope. (audited 2026-10-01 under 9g, #20; each line names the test or commit that proves it)

• A visual builder for show this question when… — pick a field, an operator, and a value from
  that field's real options. — client/tests/condition-builder.spec.ts, four-builders.spec.ts (test(e2e): one journey drives all four builders; a picked relevance and constraint match at runtime on a live CHT (#20) #28);
  ../field rules open since feat(parser): . as a subject, ../field as an alias of ${field}, function forms on . (#14) #24 (parser-dot-subject.spec.ts); searchable, grouped picker feat(ui): searchable, grouped field picker with labels; technical rows hidden; choice labels in pickers (#16) #25
  (field-picker.spec.ts). The sentence-shaped editor is 9f (T9f: Sentence-shaped inline rule editor for relevant and choice_filter; advanced panel regrouped #19), still open.
• The same for accept the answer only if… and for filtering one choice list by another answer.
  — constraint: the Validation panel feat(validation): Validation panel with presets per question type, messages beside the rule; never normalises (#18) #27 (validation-panel.spec.ts; 575 of 777 real constraints open
  fully as presets, 61 partly); choice_filter: the strip (four-builders.spec.ts).
• A builder for compute the value as…, including a decision-table form for
  if-this-then-that rules. — shared/src/xlsform/calculationBuilder.roundtrip.test.ts, geriatric build
  specs; commits 06fd035 36e6f78 4362567 c66cfcb; four-builders.spec.ts.
• Combining conditions with and / or, and one level of grouping — enough to express
  A and (B or C). — relevantParser.chain.roundtrip.test.ts, conditionReducer.test.ts
  (enter-group-mode, flat-mixed refused); commits 0b332bd 3aa66ff 2770f2a.
• Reference values from elsewhere: an earlier answer in the same form, a field on the contact,
  or a value the project's contact summary already computes. ⚠ All by picking, never by typing
  a reference expression. — pick-preexisting-values.spec.ts, form-data-passing.spec.ts;
  commits 908ddd9 be8279f e4fbab1 7a0aa2e b96e5b1; "another question" value picker feat(ui): searchable, grouped field picker with labels; technical rows hidden; choice labels in pickers (#16) #25.
• ⚠ A raw escape that preserves what it cannot model. An expression outside the builder's
  grammar must be editable as text and must survive an open-and-save byte-identically.
  — the parse → serialize self-check (relevantParser.selfSubject.roundtrip.test.ts, presets.test.ts),
  scripts/corpus-sweep.mjs identical to master on every slice, 0 / 3919 cells drift (feat(parser): . as a subject, ../field as an alias of ${field}, function forms on . (#14) #24, feat(validation): Validation panel with presets per question type, messages beside the rule; never normalises (#18) #27).

Not in scope. Grouping beyond one level. Deeper nesting multiplies the precedence and polarity
surface for very little expressive gain, and an expression that complex belongs in a computed field
instead.

Acceptance.

1. Every value in every builder can be picked; no path requires typing an identifier or a
   reference expression. — met in the inline strip and the Validation panel (feat(ui): searchable, grouped field picker with labels; technical rows hidden; choice labels in pickers (#16) #25, feat(validation): Validation panel with presets per question type, messages beside the rule; never normalises (#18) #27); the modal's
   optional custom-name escape goes with 9f (T9f: Sentence-shaped inline rule editor for relevant and choice_filter; advanced panel regrouped #19).
2. An expression the builder cannot represent round-trips byte-identically. — feat(parser): . as a subject, ../field as an alias of ${field}, function forms on . (#14) #24, feat(validation): Validation panel with presets per question type, messages beside the rule; never normalises (#18) #27 (see above).
3. An automated test drives all four builders and asserts the emitted cells on disk.
   — client/tests/four-builders.spec.ts (test(e2e): one journey drives all four builders; a picked relevance and constraint match at runtime on a live CHT (#20) #28).
4. A condition authored through the picker matches at runtime on a live instance — verified with
   real data, not by reading the generated expression. — client/tests/live-instance-check.spec.ts (test(e2e): one journey drives all four builders; a picked relevance and constraint match at runtime on a live CHT (#20) #28):
   deployed with cht-conf 6.5.0 inside the image to the local CHT 5.2.0 instance; as the CHW the question
   hides, shows after "Pass", rejects 25 with the authored message, accepts 10 → report
   01a0f7da-9c2b-766d-90aa-3aabfd8dd6be (2026-10-01).

Epic status (2026-10-01). Sub-issues: #15 (9b) PR #23 · #14 (9a) PR #24 · #16 (9c) PR #25 · #17 (9d) PR #26 ·
#18 (9e) PR #27 · #20 (9g) PR #28 · #19 (9f) open. Plan and 777-rule counts:
docs/plans/9_complex_logic_calculation_relevant_constraint/README.md on branch
9_complex_logic_calculation_relevant_constraint. Merge order for the stacked PRs: #23 → #24 → #25 → #26 → #27 → #28.