fix: qualify column names in PerfMetric upsert to avoid PG ambiguity

[SAY-5]

📝 变更描述 / Description

PostgreSQL 在 ON CONFLICT DO UPDATE SET 中将未限定的列名（如 generation_ms）视为既可指目标表列，也可指 EXCLUDED.generation_ms，触发 column reference is ambiguous (SQLSTATE 42702)，导致 failed to flush perf metric bucket 日志刷屏，性能指标无法写入。

修复方法：在 UpsertPerfMetric 的 gorm.Expr 累加表达式中显式使用 perf_metrics.<col> 限定符，明确引用目标表的现有值。MySQL 与 SQLite 同样接受 tablename.column 形式，无兼容性影响。

🚀 变更类型 / Type of change

• 🐛 Bug 修复 (Bug fix)

🔗 关联任务 / Related Issue

• Closes column reference "generation_ms" is ambiguous (SQLSTATE 42702) #4683

✅ 提交前检查项 / Checklist

• 人工确认
• 非重复提交
• Bug fix 说明
• 变更理解
• 范围聚焦
• 本地验证: go build ./model/ 与 go vet ./model/ 通过
• 安全合规

📸 运行证明 / Proof of Work

$ go vet ./model/
$ go build ./model/
(no output)

生成的 SQL 片段（PG）由

ON CONFLICT (...) DO UPDATE SET generation_ms = generation_ms + 123

变为

ON CONFLICT (...) DO UPDATE SET generation_ms = perf_metrics.generation_ms + 123

Summary by CodeRabbit

• Bug Fixes
  • Improved reliability of performance metric aggregation in database operations by ensuring proper column reference handling during conflict resolution.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 9a7f61c7-9695-4753-bb6f-2a9feb2e9f61

📥 Commits

Reviewing files that changed from the base of the PR and between a7475a1 and faa0f14.

📒 Files selected for processing (1)

• model/perf_metric.go

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Walkthrough

The UpsertPerfMetric function now qualifies all seven accumulated metric column references with the perf_metrics. table prefix in the ON CONFLICT UPDATE clauses. This resolves SQL ambiguity errors when the database cannot determine which table owns an unqualified column name in the conflict resolution expression.

Changes

SQL Column Reference Qualification

Layer / File(s)	Summary
Qualified Column References model/perf_metric.go	All conflict update clauses now reference columns as perf_metrics.request_count, perf_metrics.success_count, perf_metrics.total_latency_ms, perf_metrics.ttft_sum_ms, perf_metrics.ttft_count, perf_metrics.output_tokens, and perf_metrics.generation_ms to eliminate column ambiguity in the upsert operation.

Estimated Code Review Effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 A column stood confused and lost,
Not sure which table paid the cost,
But with a prefix clear and bright,
perf_metrics. made queries right! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: qualifying column names in PerfMetric upsert to resolve PostgreSQL ambiguity errors.
Linked Issues check	✅ Passed	The PR directly addresses issue #4683 by qualifying column names with perf_metrics prefix to resolve SQLSTATE 42702 ambiguity errors in ON CONFLICT DO UPDATE clauses.
Out of Scope Changes check	✅ Passed	All changes are focused on fixing the ambiguous column reference issue in UpsertPerfMetric; no unrelated modifications are present.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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