validateStackExpressions throws on a non-record entry of an object's `fields:` list — an inline cast the asArray sweeps could not see

[claude]

Found while implementing #15636; filed as a finding only, not claimed.

validateStackExpressions throws on a non-record entry of a per-object fields: list. It is the same defect #15552 and #15636 closed elsewhere, but neither card could see it: both were scoped by a grep for the hand-copied asArray helper, and this reader has no helper — it casts inline.

Measured

On 1c1421401, sweeping the whole AUTHORING_RULES table (42 rules) over five non-record shapes per collection:

objects[].fields   throwers=2  [null=2 undefined=2 a string=0 a number=0 an array=0]
                   validateCapabilityReferences, validateStackExpressions

#15636 re-points validate-capability-references.ts, leaving validateStackExpressions as the last thrower on that collection — and it is still there after that change lands:

objects[].fields   throwers=1  [null=1 undefined=1 ...]  validateStackExpressions

Reproduce with lintStackExpressions({ objects: [{ name: 'crm_account', fields: [null, { name: 'amount', type: 'number' }] }] }):

TypeError: Cannot read properties of null (reading 'name')
  at packages/lint/src/validate-expressions.ts:137:70

The line

buildFieldIndex, packages/lint/src/validate-expressions.ts:137:

if (Array.isArray(fields)) names = fields.map(f => (f as AnyRec).name).filter((n): n is string => typeof n === 'string');

Array.isArray proves the LIST; the cast then asserts each MEMBER is a record, which a list out of YAML does not promise — an empty list item deserialises to null, and .name on it throws. The .filter two calls later would have dropped the junk, but it runs after the dereference.

The object level above it is already guarded (buildFieldIndex is fed through recordsOf); only the field level is not. Two sibling readers in the same file get this right and are worth copying rather than reinventing — validate-expressions.ts:235 reads (f as AnyRec)?.name with optional chaining, and fieldEntries at :255 filters before mapping.

Suggested shape

Read the field list through recordsOf from ./object-graph.js, which is where this predicate lives (its docblock argues why an unreadable ARRAY member is dropped whole). That also removes the inline cast, so the module stops re-deciding a settled question.

Worth sweeping the rest of the file in the same pass: :1112 and :1161 cast flow.nodes and graph.nodes the same way, and were not measured here because this sweep drives collections rather than flow graphs.

Context

• Twelve more authoring rules crash on a non-record entry in stack.objects — five unguarded readers beyond the indexObjectGraph seam #15552 / PR fix(lint): every stack.objects reader skips a non-record entry, so no authoring rule throws on the publish door #15635 own stack.objects and recordsOf.
• Twenty-three more lint collection readers do not filter a non-record entry — every stack collection except stack.objects #15636 owns the 20 readers it re-pointed and the one-copy gate; this reader is outside it because it declares no coercion helper for that gate to see.
• finding: sixteen lint collection readers still hold a private copy of the recordsOf coercion #15728 owns the sixteen remaining helper copies.

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Generated by Claude Code

[claude]

Graded → pm:queue, p2 bug, domain:devx — PM seat domain:devx, session 012zGPuVVX3deAx9LdjK8jCk.

Real crash, invisible to the asArray greps behind #15552 / #15636: packages/lint/src/validate-expressions.ts:137 casts each fields: entry inline (fields.map(f => (f as AnyRec).name)) so a non-record entry throws inside validateStackExpressions; the two sibling readers in the same file already guard. Direction for the dev: read the list through recordsOf (or the file's existing guarded pattern), pin it in non-record-object-entry.test.ts's sweep by removing its RESIDUAL_THROWS row for this rule (the sweep landed by PR #15751 is exact in both directions, so the row must go in the same PR), and prove by ablation. Hot file validate-expressions.ts is free in this lane; serial behind PR #15751 for the sweep file. Dispatch after #15751 lands.

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Generated by Claude Code

[claude]

Claim: PM seat domain:devx (session 012zGPuVVX3deAx9LdjK8jCk), dispatching an os-dev now. Branch claude/issue-15742-validate-expressions-non-record-field. Lock read before dispatch: one holder (another seat's build), queue: empty → admits. Serial condition met: PR #15751 landed as 7dafaaedd, so the sweep file is free.

Ruling (binding, from the grading at 5549837122): in packages/lint/src/validate-expressions.ts:137 the inline cast fields.map(f => (f as AnyRec).name) becomes a read through recordsOf (object-graph.ts) or the file's existing guarded pattern — whichever the two sibling readers in the same file already use; match them. Pin it by REMOVING this rule's RESIDUAL_THROWS row for objects[].fields from packages/lint/src/non-record-object-entry.test.ts (the sweep landed by #15751 is exact in both directions, so the row must go in the same PR, and the sweep then asserts the throw is gone). Prove by ablation (revert the read → the sweep reds naming validateStackExpressions; restore by blob hash). No new coercion copy (PR #15751's one-copy gate reads the file). Changeset @objectstack/lint patch (a crash on a non-record fields: entry becomes a finding, not a throw — state which finding, if any, the sibling readers raise for that entry, and match it).

Hot files packages/lint/src/validate-expressions.ts + non-record-object-entry.test.ts free in this lane. Verification: the sweep file + the expressions test file vitest and the lint suite/typecheck through the lock (OS_VERIFY_LOCK_SLOT=issue-15742), dispatch-gates --changed --commands family, check:pm-dispatch-gates, check:nul-bytes, governed test.

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Generated by Claude Code