Second install rewrites default-valued nodes: default-suppression makes the stored node differ from the authored file, so the unchanged-skip misses #2271

What happens

A second install of the same package rewrites nodes whose content is default-valued — observed on PensionFund/Currency/{CHF,EUR,USD} (3 nodes rewritten, expected 0). It is the deploy-flicker the idempotence pin exists to catch.

Mechanism

Currency.DecimalPlaces carries a C# initializer = 2 (PensionFund/Currency/Source/Currency.cs), and all three instance files author "decimalPlaces": 2.

1. Once the Currency NodeType compiles, its content type is registered.
2. The installer therefore materialises the instance as a typed Currency rather than an untyped JsonElement, and re-serialises it.
3. Default-suppression drops the property whose value equals the type's default.
4. The stored node now differs from the authored file — so the unchanged-skip misses, and the next install rewrites it.

Year/2024 and every Position/* round-trip clean. The three that churn are exactly the three whose content is default-valued.

Why it is intermittent — and why that matters

It is invisible until the NodeType compiles. That is why the gate reported it inconsistently within one hour tonight:

• one run: STALE allow entry (now passing — remove it): PensionFund idempotence
• the very next: GATE FAILED — idempotence: PensionFund — 1 new failure(s)

Both reports are correct. I removed the allow entry on the first and had to restore it on the second — recorded at the entry so the next person does not repeat it. A single green run is not evidence this is gone.

Why it is surfacing now

#2063's discovery fix means the gate now finds PensionFund's 5 NodeTypes where it previously found 0 (the BOM hid them). So the compile happens, step 1 above becomes reachable, and a defect that was always present becomes intermittently visible.

Suggested direction

The write path should compare against what was authored, not against a re-serialisation of the materialised value — or default-suppression must not apply on the install round-trip. Related and possibly the same root: #2266, where the installer logs "the file's authored content could not be re-read — installing the materialised value, which may carry another package's defaults." Both are the installer preferring a materialised value over the authored one.

Currently carried as known debt in .github/samples-gate.allow (PensionFund idempotence).