feat(mcp): record safe tool input names

[gesh]

💡 Motivation and Context

MCP server owners need to measure which input names agents use. This must not expose argument values or unknown field names.

This PR ports the input-name and alias contract from @posthog/mcp 0.19.0 and 0.20.0. It adds $mcp_input_keys, $mcp_input_aliases_used, and a helper for custom dispatchers.

💚 How did you test it?

• uv run pytest -q posthog/test/mcp --timeout=30
• uv run ruff check posthog/mcp posthog/test/mcp/test_tool_input.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 keeps schemas isolated by session and redacts unknown names by default.

---

Created with PostHog Desktop

[github-actions]

posthog-python Compliance Report

Date: 2026-10-02T08:21:15.767961+00:00
Duration: 259774ms

✅ 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	✅	516ms
Endpoint And Method.Does Not Use Legacy Endpoints	✅	511ms
Required Headers.Has Authorization Bearer Header	✅	510ms
Required Headers.Has Content Type Json	✅	514ms
Required Headers.Has Posthog Sdk Info Format	✅	511ms
Required Headers.Has Posthog Attempt Header	✅	512ms
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	✅	510ms
Body Format.No Api Key In Body	✅	512ms
Body Format.No Sent At In Body	✅	510ms
Event Format.Event Has Required Root Fields	✅	511ms
Event Format.Event Uuid Is Valid	✅	510ms
Event Format.Event Timestamp Is Rfc3339	✅	511ms
Event Format.Non Utc Event Timestamp Is Converted To Utc	✅	517ms
Event Format.Distinct Id Is String	✅	510ms
Event Format.Distinct Id At Root Not Properties	✅	511ms
Event Format.Custom Properties Preserved	✅	511ms
Event Format.Set Properties Preserved	✅	511ms
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	✅	515ms
Event Format.Event Uuid Is Valid Batch	✅	514ms
Event Format.Event Timestamp Is Rfc3339 Batch	✅	514ms
Event Format.Distinct Id Is String Batch	✅	514ms
Event Format.Distinct Id At Root Not Properties Batch	✅	514ms
Event Format.Custom Properties Preserved Batch	✅	514ms
Event Format.Set Properties Preserved Batch	✅	514ms
Event Format.Set Once Properties Preserved Batch	✅	513ms
Event Format.Groups Properties Preserved Batch	✅	514ms
Event Format.Sdk Generates Uuid If Not Provided Batch	✅	516ms
Batch Behavior.Multiple Events In Single Batch	✅	520ms
Batch Behavior.Batch Envelope Smoke	✅	515ms
Batch Behavior.Flush With No Events Sends Nothing	✅	507ms
Batch Behavior.Flush At Triggers Batch	✅	1012ms
Batch Behavior.Created At Reflects Batch Creation Time	✅	511ms
Deduplication.Generates Unique Uuids	✅	517ms
Deduplication.Different Events Same Content Different Uuids	✅	513ms
Deduplication.Preserves Uuid On Retry	✅	6519ms
Deduplication.Preserves Timestamp On Retry	✅	6517ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	6523ms
Deduplication.No Duplicate Events In Batch	✅	519ms
Header Behavior On Retry.Attempt Header Starts At One	✅	511ms
Header Behavior On Retry.Attempt Header Increments On Retry	✅	13530ms
Header Behavior On Retry.Request Id Preserved On Retry	✅	6521ms
Header Behavior On Retry.Different Requests Have Different Request Ids	✅	3022ms
Header Behavior On Retry.Request Timestamp Changes On Retry	✅	6521ms
Response Format Validation.Success Response Has Uuid Keyed Results	✅	511ms
Response Format Validation.Success Response Has Ok For Each Event	✅	517ms
Response Format Validation.Success No Retry After When All Ok	✅	514ms
Response Format Validation.Success Retry After Present When Retry Events	✅	1516ms
Response Format Validation.Success No Retry After When Drop Only	✅	515ms
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	✅	8525ms
Retry Behavior.Retries On 504	✅	6521ms
Retry Behavior.Retryable Errors Have Retry After	✅	3518ms
Retry Behavior.Respects Retry After On Retryable Error	✅	11523ms
Retry Behavior.Does Not Retry On 400	✅	2513ms
Retry Behavior.Does Not Retry On 401	✅	2515ms
Retry Behavior.Does Not Retry On 402	✅	2515ms
Retry Behavior.Does Not Retry On 413	✅	2514ms
Retry Behavior.Does Not Retry On 415	✅	2516ms
Retry Behavior.Non Retryable Errors Have No Retry After	✅	2516ms
Retry Behavior.Implements Backoff	✅	22538ms
Retry Behavior.Max Retries Respected	✅	22537ms
Partial Batch Handling.Handles 200 Full Success	✅	2514ms
Partial Batch Handling.Handles 200 With All Ok	✅	3516ms
Partial Batch Handling.Does Not Retry Dropped Events	✅	3518ms
Partial Batch Handling.Does Not Retry Limited Events	✅	3518ms
Partial Batch Handling.Prunes Ok Events On Partial Retry	✅	6524ms
Partial Batch Handling.Prunes Dropped Events On Partial Retry	✅	6521ms
Partial Batch Handling.Retries Only Retry Events From Partial	✅	6525ms
Partial Batch Handling.Partial Retry Preserves Uuids	✅	6523ms
Partial Batch Handling.Partial Retry Attempt Header Increments	✅	6523ms
Partial Batch Handling.Partial Retry Request Id Preserved	✅	6523ms
Partial Batch Handling.Respects Retry After On Partial	✅	8523ms
Partial Batch Handling.Unknown Result Treated As Terminal	✅	3517ms
Partial Batch Handling.Mixed Ok Drop Limited No Retry	✅	3523ms
Compression.Sends Gzip Content Encoding	✅	511ms
Compression.No Content Encoding When Disabled	✅	510ms
Compression.Compressed Body Is Decompressible	✅	512ms
Error Handling.Does Not Retry On Unknown 4Xx	✅	2513ms
Event Options.Cookieless Mode Override	✅	511ms
Event Options.Disable Skew Correction Override	✅	511ms
Event Options.Process Person Profile Override	✅	511ms
Event Options.Product Tour Id Override	✅	510ms
Event Options.Unset Options Omitted	✅	511ms
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	✅	512ms
Geoip And Historical Migration.Historical Migration Absent By Default	✅	510ms

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	✅	510ms
Identity.Capture Ai Event Has Uuid	✅	510ms
Identity.Capture Ai Keeps Supplied Uuid	✅	511ms
Timestamp Format.Non Utc Event Timestamp Is Converted To Utc	✅	512ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	12ms
Request Payload.Flags Request Uses V2 Query Param	✅	11ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	9ms
Request Payload.Flags Request Omits Authorization Header	✅	8ms
Request Payload.Token In Flags Body Matches Init	✅	7ms
Request Payload.Groups Round Trip	✅	8ms
Request Payload.Groups Default To Empty Object	✅	8ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	7ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	8ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	7ms
Request Lifecycle.No Flags Request On Init Alone	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	508ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	14ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	8ms
Retry Behavior.Retries Flags On 502	✅	311ms
Retry Behavior.Retries Flags On 504	✅	315ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	512ms

Feature_Flags_Local_Evaluation Tests

✅ 4/4 tests passed

View Details

Test	Status	Duration
Versioned Boolean Matching.Matching Version Missing	✅	61ms
Versioned Boolean Matching.Matching Version 1	✅	55ms
Versioned Boolean Matching.Matching Version 2	✅	54ms
Versioned Boolean Matching.Version Only Reload 1 2 1 2 Missing	✅	28ms

[greptile-apps]

[Medium risk] Adds safe input field name recording to MCP tool-call events.

The PR should not merge until declared input names are captured for referenced standalone FastMCP schemas.

_{Reviews (2) · Last reviewed commit: "fix(mcp): scope input schemas to tool ca..."}

[lucasheriques]

The no-values design and the analytics-key filtering hold up. Approving, with a few parity questions, since the same property would carry different data in Python and JS.