Check every index read in the app and the embed: the flag is on

[adamjohnwright]

Part of #345. This is the last of the app's noUncheckedIndexedAccess findings. The flag is now on in tsconfig.app.json and projects/reactome-diagram-element/tsconfig.app.json, so the builds enforce it.

The two files

• render.component.ts (62): the figure renderer's geometry. Most findings came from a few reads (a chord's ends, a polygon's previous vertex, a segment's ends, the arrow's tip). Each now has a guard that can't fire on real data, because every index is in range by construction. The four-edge clip loop gets a pair type. Exports take const [instance] = instances.
• diagram.service.ts (23): closest-to-average, pick, the normal-pathway id, CHEBI ids, sub-pathway pairs, homomer children, compartment insets (now over a typed list of sides, in the same order as Object.keys gave), polymer units, link ends, and the legend's node/reaction pairing.
• No non-null assertions were added (lint is at its baseline).

Templates

tsc doesn't check templates, but with the flag on, Angular's strict template checking does. It found five more:

• Four passed a sample's expression value (exp[i], values[i]) to cr-expression-tag, which isn't built for a missing one (a GSA label lookup and the colour scale would break). Those cells now read the value with @let and draw the tag only when there is one. The index is in range in practice, so nothing changes on screen.
• The fifth, the found table's resource column id, falls back to the same entities-{resource} id it's computed from.

Behaviour

• One stated change: a diagram link with no input or output already threw on link.inputs[0].id. It now throws Link {id} has no input or no output.
• CHEBI ids: an identifier without a chebi: prefix used to add undefined to the set of ids looked up. It's now left out, so the page no longer asks EBI for /compound/NaN/structure/.
• After review: pick throws only for an empty list (one caller picks undefined on purpose); an EntitySet link with no ends reaches the named error instead of being filtered out; closestToAverage over no positions throws, as it did, with a message, instead of placing a shadow at NaN.

The check moves on

scripts/check-indexed-access.mjs now counts the projects that don't have the flag yet: the workspace libraries reactome-table (66) and reactome-gsa-form (18), 84 findings in 10 files. When they reach zero, the flag goes into tsconfig.json and the check goes. (tsconfig.spec.json stays out: it can't resolve vitest/globals, as check-types.mjs notes.)

Tests

• App config proven: an added xs[0].length fails check:types with TS2532.
• Builds: npm run build and npm run build:embed with the flag: both complete.
• Full e2e suite locally: 388 passed, plus the 6 tests that skip themselves.
• Unit tests: 538 passed.
• Render tests: ran live against the render service in the pre-push hook: ok.
• Gates: check:lint and check:indexed unchanged at the baseline.

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