[BUG][UI]: Metrics top performers panel incorrect display of zero values, timestamps, and unexecuted entity success rates

[shoummu1]

🐞 Bug Summary

Five related bugs found in the top performers metrics panel, discovered during investigation of #3580:

1. build_top_performers() loses 0.0 metric values — metrics_common.py uses falsy checks (if result.success_rate) which coerce a genuine 0.0 success rate (100% failure) or 0.0 avg response time to None, losing the distinction between "no data" and an actual zero value.

2. Dead != 'N/A' guard in template — metrics_top_performers_partial.html checks avg_response != 'N/A', but avgResponseTime is Optional[float] and can only be None or a float — never the string 'N/A'. The branch is unreachable.

3. Dead != 'Never' guard in template — similarly, the template checks last_exec != 'Never', but lastExecution from jsonable_encoder is either None or an ISO datetime string, never the string 'Never'. The branch is unreachable.

4. Raw ISO datetime display in "Last Used" column — the template renders {{ last_exec }} verbatim, producing unreadable output like 2024-01-15T10:30:00.000000 in the UI instead of a human-friendly format like 2024-01-15 10:30.

5. successRate: None displays as 0.0% with a red error badge — the or 0 fallback collapses None (no executions yet) into 0, making a tool with no data look like it has a 100% failure rate. Should display "N/A" with no badge, matching the avgResponseTime treatment.

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🧩 Affected Component

• mcpgateway - UI (admin panel)
• mcpgateway - API

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🔁 Steps to Reproduce

1. Navigate to the Admin UI → Metrics tab → Top Performers panel
2. Observe the "Last Used" column — ISO timestamps are displayed raw (e.g. 2024-01-15T10:30:00.000000)
3. Observe the "Success Rate" column for a tool that has never been executed — it shows 0.0% with a red badge instead of N/A
4. For bug 1: register a tool with 0% success rate — the panel treats it as if it has no metrics at all

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🤔 Expected Behavior

1. A success_rate or avg_response_time of 0.0 should be preserved and displayed as 0.0, not treated as missing data.
2. The != 'N/A' guard should be removed (dead code); None check is sufficient.
3. The != 'Never' guard should be removed (dead code); falsy check on None is sufficient.
4. The "Last Used" column should display a human-readable datetime like 2024-01-15 10:30 instead of a raw ISO string.
5. The "Success Rate" column should display N/A (no badge) for entities with no execution data, not 0.0% with a red error badge.

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📓 Logs / Error Output

No stack traces. These are silent display/logic bugs.

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🧠 Environment Info

Key	Value
Version or commit	main
Runtime	Python 3.11, Gunicorn
Platform / OS	any
Container	any

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🧩 Additional Context (optional)

• Affects mcpgateway/utils/metrics_common.py (build_top_performers function)
• Affects mcpgateway/templates/metrics_top_performers_partial.html (avg response, success rate, last execution columns)

[crivetimihai]

Thanks @shoummu1 — good catch on the falsy-check conflation of 0.0 with None in build_top_performers(). The 5 bugs are well-documented. These are display/logic issues with no data loss or security impact. Tagging as SHOULD for Release 1.1.0.