feat(mcp): manage disposition metrics via update_agent (PRO-1949)

[prat11m]

What

Adds post-call disposition metric management to the MCP update_agent tool. Previously dispositionMetrics (postCallAnalyticsConfig) was unreachable via MCP — the tool only exposed the free-form callDispositionConfig string.

Two new params on update_agent:

• add_disposition_metrics — [{ identifier, prompt, metric_type, choices? }], upsert by identifier
• remove_disposition_metrics — [identifier]

The backend only supports full-array replace on postCallAnalyticsConfig (no per-metric endpoint), so the tool masks that: it reads the branch's current metrics, applies remove-then-add, and writes the whole array back — preserving summaryPrompt and untouched metrics. Callers just say "+ these / − those".

How

• Read (draft-aware): readResolvedConfig in versioning.ts uses GET /agent/:id?draftId=|versionId= — the only path that resolves section blocks into a flat config (blocks store section references, not inline content).
• Validate locally (mirrors backend transformPostCallAnalyticsConfig): identifier ^[a-z0-9_]+$, ENUM requires non-empty choices, no duplicate identifiers — clear errors before the round-trip.
• Write: full postCallAnalyticsConfig via the existing draft PUT, with expectedRevision passed for optimistic concurrency when a draft is already open (backend 409s on a conflicting analytics-section edit instead of clobbering).
• get_agent now lists current dispositionMetrics (read from _resolvedConfig, since the agent DTO strips postCallAnalyticsConfig).

Metric shape: { identifier, dispositionMetricPrompt, dispositionMetricType ∈ STRING|BOOLEAN|INTEGER|ENUM|DATETIME, choices? (ENUM) }.

What to test

• update_agent with add_disposition_metrics (each type; ENUM with/without choices) on a branch → get_branch_draft / test_agent --include_draft shows them.
• Re-adding an existing identifier updates it (upsert); remove_disposition_metrics drops it.
• get_agent lists the live metrics.
• Concurrent edit on an open draft's analytics section surfaces the expectedRevision conflict.

What to validate

• Draft-aware read on a non-live branch and on a branch with a pre-existing open draft whose analytics differ from head (the one path not yet exercised live).
• summaryPrompt is preserved when only metrics change.

Env vars

None.

Deployment

Plain merge-deploy (rebuild + redeploy MCP server). No migrations, no config.

Notes

Related backend/PCA bugs tracked in PRO-1949 (weak callDispositionConfig validation, no granular metric API, ...pca passthrough) — out of scope for this PR.

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