[finding] `os validate --json` never carries the four inline non-blocking warnings the text summary prints (no objects / no apps+plugins / missing manifest.id / missing manifest.namespace)

[os-elon]

Split out of #10504 while checking its brief's fencing item #2 ("check the --json path for the same drop"). Filed unassigned — not routed, not graded.

Measured

On the blank-shaped zero-apps scaffold at current main head, comparing os validate (text) against os validate --json for the identical config:

Text output includes:

 ⚠ No apps or plugins defined — this stack may not do much
 ⚠ Missing manifest.namespace — required for multi-app hosting

--json output for the same run:

{
 "valid": true,
 "stats": { "objects": 1, ..., "apps": 0, ... },
 "warnings": [],
 ...
}

warnings is empty. Not a zero-vs-absent-key nuance (the stats.apps: 0 key is present fine, per #10504's own scope) — the four advisories are structurally unreachable in the JSON path. In packages/cli/src/commands/validate.ts, the JSON payload is emitted and the command returns before the block that computes them:

if (flags.json) {
 await emitJson({ ..., warnings: [...ruleAdvisories, ...docWarnings, ...unknownKeyWarnings, ...capProviderWarnings], ... });
 return; // ← json path exits here
}

// 5. Warnings (non-blocking) — everything below only ever feeds the text path
const warnings: string[] = [];
...
if (stats.objects === 0) warnings.push('No objects defined — this stack has no data model');
if (stats.apps === 0 && stats.plugins === 0) warnings.push('No apps or plugins defined — this stack may not do much');
if (!config.manifest?.id) warnings.push('Missing manifest.id — required for deployment');
if (!config.manifest?.namespace) warnings.push('Missing manifest.namespace — required for multi-app hosting');

This is the exact "computed, then discarded" shape the file's own comment (line ~81-82, on unknownKeyWarnings) says it already had to fix once — recurring here for these four checks. A CI script consuming os validate --json to gate on advisories (the documented reason --json exists) cannot see any of these four, regardless of whether the underlying condition is true.

This lane has already seen a text/--json divergence of this general shape on os compile (#10678/#10912).

Suggested landing

packages/cli/src/commands/validate.ts — hoist the four conditions (or compute a shared structuralWarnings: string[] once) above the if (flags.json) branch, the same move already made for unknownKeyWarnings, and include it in both the JSON warnings array and the text-path warnings array.