feat(mcp): capture server build metadata

[gesh]

💡 Motivation and Context

MCP server owners need to connect events to the exact code that handled each request. MCP server metadata only identifies the release version.

This PR ports server_build from @posthog/mcp 0.21.0. Automatic instrumentation and custom dispatchers record the value as $mcp_server_build on all MCP events.

PostHogMCP.capture() also adds the configured value to custom events. An event-specific value takes precedence over the configured value.

from posthog.mcp import MCPAnalyticsOptions, instrument

instrument(
    server,
    posthog,
    MCPAnalyticsOptions(server_build="git-sha-or-image-digest"),
)

💚 How did you test it?

• uv run pytest -q posthog/test/mcp --timeout=30
• uv run ruff check posthog/mcp posthog/test/mcp/test_posthog_mcp.py posthog/test/mcp/test_features_m4.py
• uv run mypy --no-site-packages --config-file mypy.ini posthog/mcp | uv run mypy-baseline filter
• make public_api_check

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Codex implemented the agreed Python port. The implementation validates the value during setup and applies it to exception events.

---

Created with PostHog Desktop

[github-actions]

posthog-python Compliance Report

Date: 2026-09-30T14:13:07.473495+00:00
Duration: 260002ms

✅ All Tests Passed!

121/121 tests passed

---

Capture_V1 Tests

✅ 95/95 tests passed

View Details

Test	Status	Duration
Endpoint And Method.Targets V1 Endpoint	✅	519ms
Endpoint And Method.Does Not Use Legacy Endpoints	✅	511ms
Required Headers.Has Authorization Bearer Header	✅	511ms
Required Headers.Has Content Type Json	✅	513ms
Required Headers.Has Posthog Sdk Info Format	✅	511ms
Required Headers.Has Posthog Attempt Header	✅	510ms
Required Headers.Has Posthog Request Id	✅	511ms
Required Headers.Has Posthog Request Timestamp	✅	510ms
Required Headers.Has User Agent	✅	511ms
Body Format.Body Has Created At And Batch	✅	511ms
Body Format.No Api Key In Body	✅	510ms
Body Format.No Sent At In Body	✅	511ms
Event Format.Event Has Required Root Fields	✅	511ms
Event Format.Event Uuid Is Valid	✅	511ms
Event Format.Event Timestamp Is Rfc3339	✅	511ms
Event Format.Non Utc Event Timestamp Is Converted To Utc	✅	516ms
Event Format.Distinct Id Is String	✅	511ms
Event Format.Distinct Id At Root Not Properties	✅	510ms
Event Format.Custom Properties Preserved	✅	511ms
Event Format.Set Properties Preserved	✅	510ms
Event Format.Set Once Properties Preserved	✅	510ms
Event Format.Groups Properties Preserved	✅	511ms
Event Format.Sdk Generates Uuid If Not Provided	✅	511ms
Event Format.Event Has Required Root Fields Batch	✅	514ms
Event Format.Event Uuid Is Valid Batch	✅	514ms
Event Format.Event Timestamp Is Rfc3339 Batch	✅	517ms
Event Format.Distinct Id Is String Batch	✅	515ms
Event Format.Distinct Id At Root Not Properties Batch	✅	515ms
Event Format.Custom Properties Preserved Batch	✅	515ms
Event Format.Set Properties Preserved Batch	✅	515ms
Event Format.Set Once Properties Preserved Batch	✅	513ms
Event Format.Groups Properties Preserved Batch	✅	515ms
Event Format.Sdk Generates Uuid If Not Provided Batch	✅	520ms
Batch Behavior.Multiple Events In Single Batch	✅	518ms
Batch Behavior.Batch Envelope Smoke	✅	516ms
Batch Behavior.Flush With No Events Sends Nothing	✅	508ms
Batch Behavior.Flush At Triggers Batch	✅	1011ms
Batch Behavior.Created At Reflects Batch Creation Time	✅	512ms
Deduplication.Generates Unique Uuids	✅	517ms
Deduplication.Different Events Same Content Different Uuids	✅	512ms
Deduplication.Preserves Uuid On Retry	✅	6520ms
Deduplication.Preserves Timestamp On Retry	✅	6517ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	6524ms
Deduplication.No Duplicate Events In Batch	✅	520ms
Header Behavior On Retry.Attempt Header Starts At One	✅	511ms
Header Behavior On Retry.Attempt Header Increments On Retry	✅	13523ms
Header Behavior On Retry.Request Id Preserved On Retry	✅	6520ms
Header Behavior On Retry.Different Requests Have Different Request Ids	✅	3020ms
Header Behavior On Retry.Request Timestamp Changes On Retry	✅	6521ms
Response Format Validation.Success Response Has Uuid Keyed Results	✅	512ms
Response Format Validation.Success Response Has Ok For Each Event	✅	514ms
Response Format Validation.Success No Retry After When All Ok	✅	513ms
Response Format Validation.Success Retry After Present When Retry Events	✅	1516ms
Response Format Validation.Success No Retry After When Drop Only	✅	512ms
Response Format Validation.Response Echoes Request Id	✅	512ms
Retry Behavior.Retries On 408	✅	6520ms
Retry Behavior.Retries On 500	✅	6520ms
Retry Behavior.Retries On 503	✅	8524ms
Retry Behavior.Retries On 504	✅	6517ms
Retry Behavior.Retryable Errors Have Retry After	✅	3517ms
Retry Behavior.Respects Retry After On Retryable Error	✅	11525ms
Retry Behavior.Does Not Retry On 400	✅	2514ms
Retry Behavior.Does Not Retry On 401	✅	2514ms
Retry Behavior.Does Not Retry On 402	✅	2514ms
Retry Behavior.Does Not Retry On 413	✅	2514ms
Retry Behavior.Does Not Retry On 415	✅	2514ms
Retry Behavior.Non Retryable Errors Have No Retry After	✅	2513ms
Retry Behavior.Implements Backoff	✅	22526ms
Retry Behavior.Max Retries Respected	✅	22531ms
Partial Batch Handling.Handles 200 Full Success	✅	2513ms
Partial Batch Handling.Handles 200 With All Ok	✅	3518ms
Partial Batch Handling.Does Not Retry Dropped Events	✅	3517ms
Partial Batch Handling.Does Not Retry Limited Events	✅	3516ms
Partial Batch Handling.Prunes Ok Events On Partial Retry	✅	6521ms
Partial Batch Handling.Prunes Dropped Events On Partial Retry	✅	6522ms
Partial Batch Handling.Retries Only Retry Events From Partial	✅	6519ms
Partial Batch Handling.Partial Retry Preserves Uuids	✅	6523ms
Partial Batch Handling.Partial Retry Attempt Header Increments	✅	6522ms
Partial Batch Handling.Partial Retry Request Id Preserved	✅	6518ms
Partial Batch Handling.Respects Retry After On Partial	✅	8517ms
Partial Batch Handling.Unknown Result Treated As Terminal	✅	3517ms
Partial Batch Handling.Mixed Ok Drop Limited No Retry	✅	3521ms
Compression.Sends Gzip Content Encoding	✅	511ms
Compression.No Content Encoding When Disabled	✅	510ms
Compression.Compressed Body Is Decompressible	✅	511ms
Error Handling.Does Not Retry On Unknown 4Xx	✅	2514ms
Event Options.Cookieless Mode Override	✅	511ms
Event Options.Disable Skew Correction Override	✅	511ms
Event Options.Process Person Profile Override	✅	510ms
Event Options.Product Tour Id Override	✅	510ms
Event Options.Unset Options Omitted	✅	510ms
Event Options.Options Override In Batch	✅	514ms
Geoip And Historical Migration.Geoip Disable Injected Into Properties	✅	511ms
Geoip And Historical Migration.Historical Migration Set In Body	✅	510ms
Geoip And Historical Migration.Historical Migration Absent By Default	✅	511ms

Capture_Ai Tests

✅ 5/5 tests passed

View Details

Test	Status	Duration
Routing.Capture Ai Posts To Ai Endpoint	✅	510ms
Routing.Capture Does Not Reroute Ai Named Events	✅	511ms
Identity.Capture Ai Event Has Uuid	✅	511ms
Identity.Capture Ai Keeps Supplied Uuid	✅	510ms
Timestamp Format.Non Utc Event Timestamp Is Converted To Utc	✅	511ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	11ms
Request Payload.Flags Request Uses V2 Query Param	✅	10ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	9ms
Request Payload.Flags Request Omits Authorization Header	✅	12ms
Request Payload.Token In Flags Body Matches Init	✅	10ms
Request Payload.Groups Round Trip	✅	10ms
Request Payload.Groups Default To Empty Object	✅	9ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	9ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	9ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	11ms
Request Lifecycle.No Flags Request On Init Alone	✅	4ms
Request Lifecycle.No Flags Request On Normal Capture	✅	510ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	17ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	11ms
Retry Behavior.Retries Flags On 502	✅	314ms
Retry Behavior.Retries Flags On 504	✅	314ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	514ms

Feature_Flags_Local_Evaluation Tests

✅ 4/4 tests passed

View Details

Test	Status	Duration
Versioned Boolean Matching.Matching Version Missing	✅	85ms
Versioned Boolean Matching.Matching Version 1	✅	71ms
Versioned Boolean Matching.Matching Version 2	✅	74ms
Versioned Boolean Matching.Version Only Reload 1 2 1 2 Missing	✅	42ms

[greptile-apps]

[Medium risk] Adds optional deployment identifier to MCP analytics events.

The PR appears safe to merge.

_{Reviews (2) · Last reviewed commit: "fix(mcp): preserve validated server buil..."}

[dustinbyrne]

Reviewed both MCP entry paths, validated build snapshots, exception-event attribution, truncation and final privacy hooks. The earlier review findings are addressed. No issues found.

Validation: static source review and existing CI; no tests or device runs executed for this review.

Human-driven, agent-assisted review.