DISPLAY capability probing (spike)

Spike for ADR-0024 §4: probe whether mqweb allows a queue attribute in runCommandJSON DISPLAY responseParameters instead of maintaining static safe lists in internal/adapter/mqrest/mqsc_params.go.

Problem

Some QLOCAL attributes are valid on DEFINE but rejected when requested in DISPLAY responseParameters. On IBM MQ 9.4.x mqweb this surfaces as MQWB0120E. MKurator omits those keys from drift checks today; see ATTRIBUTE_RECONCILIATION.md (e.g. share, defopts, bothresh, boqname, usage, maxmsglen).

Hand-maintained slices (queueLocalDisplayParameters) do not adapt when a newer mqweb starts supporting DISPLAY for a formerly define-only keyword.

Probe method

Issue DISPLAY for an existing local queue with a single responseParameter:

{
  "type": "runCommandJSON",
  "command": "display",
  "qualifier": "qlocal",
  "name": "<probe-queue>",
  "responseParameters": ["share"]
}

Interpretation:

Outcome	Meaning
overallCompletionCode 0 and parameters returned	Attribute is displayable — safe to add to drift checks
Message contains MQWB0120E	Attribute is define-only on this mqweb/QM
AMQ8147E / not found	Probe queue missing — fix probe setup, not attribute capability

Implementation: Client.ProbeQueueLocalAttributeDisplayable in internal/adapter/mqrest/display_probe.go.

Wired probing (ADR-0024 §4)

All QueueLocalDefineOnlyCandidates are probed at runtime via queueLocalProbedDisplayCandidates and the client cache in display_probe_cache.go. ResolveQueueDriftCheckKeys and GetQueue for local queues include each candidate in DISPLAY/drift only when mqweb reports it displayable.

Spike outcomes on mqweb 9.4.x (Docker MQ 9.4.5.1-r1):

Attribute	Static table (9.4.x)	Probe outcome
maxmsglen	DEFINE-only (MQWB0120E)	Not displayable on Docker MQ 9.4.5.1-r1 (integration CI) — confirms static omission
share	DEFINE-only (MQWB0120E)	Displayable on Docker MQ 9.4.5.1-r1 — static safe list is stale for this fix level

Other candidates (defopts, bothresh, boqname, usage) are probed live; outcomes are mqweb-version-dependent (integration tests log results).

The share result is why ADR-0024 §4 favours runtime probing over hand-maintained queueLocalDisplayParameters: mqweb fix packs can enable DISPLAY for keywords that older docs and tables still list as define-only.

define share / define maxmsglen on QLOCAL still succeed when DISPLAY via responseParameters is blocked. Drift for blocked keys remains deferred until probe (or manual test) shows DISPLAY support on the target mqweb level.

Future wiring

Per ADR-0024 §4, remaining work:

1. Optionally run probes once per QueueManagerConnection at Ready and surface displayable sets on QMC status (today: lazy probe on first local GetQueue).
2. Build DISPLAY responseParameters from desired keys ∩ displayable set.

Candidates for bulk probe: QueueLocalDefineOnlyCandidates in display_probe.go.

Verification

# Unit (always)
go test ./internal/adapter/mqrest/... -run Probe -count=1

# Live mqweb (optional)
KURATOR_INTEGRATION_MQ=1 task mq:integration:up
go test -tags=integration ./test/integration/mq/... -run ProbeQueueLocalAttribute_DisplayProbeMechanism -count=1