fix: accept native FME flag create aliases and align leftover agent docs

[ravindraharness]

Description

Follow-up to #806 (feat: FME dual-mode Harness-native scope migration).

#806 already wired Harness-native fme_feature_flag create / update (JSON Merge Patch) / archive / unarchive, plus kill / restore / reallocate aliases onto /fme/api/v4/feature-flag-definitions/{name}/…. This PR does not re-implement those routes. It lands leftover agent-facing create input gaps that still produce wrong calls after that merge.

Why this follow-up exists

Agents that already know the legacy create contract pass traffic_type_id at the top level (it is a path param on Split v2). Native v4 requires trafficType in the JSON body, not in the path. After #806, that top-level field was ignored and create failed with “trafficType is required in body”, even though the caller had a traffic type. Native create could also POST { name: undefined } if body.name was omitted.

feature-flag-rollout no longer tells agents that native definitions or kill/restore are unimplemented. On this branch, fme_rollout_status.list in native mode is still called out as a remaining gap (wired separately in #838).

Key implementation changes

• src/registry/toolsets/feature-flags.ts — native create bodyBuilder resolves trafficType from body.trafficType, then traffic_type_id, traffic_type, or body.traffic_type. Missing traffic type or missing name throws a clear error. The wire body is still { name, trafficType, description?, tags?, owners? } on POST /fme/api/v4/feature-flags (no traffic type in the path). Tag wrapping continues to use normalizeFmeTags.
• src/prompts/feature-flag-rollout.ts — native-mode caveat no longer claims definitions or kill/restore are unimplemented.
• tests/registry/feature-flags.test.ts — traffic_type_id → body.trafficType and missing-name fail-closed.
• tests/registry/registry.test.ts — fixture proving ResolvedRoute.headers override EndpointSpec.headers (route wins). Dispatch merge itself shipped in feat: [FME-17249]: FME dual-mode Harness-native scope migration #806; this is the missing unit coverage.

This PR does not change docs/testing/fme_feature_flag/test_plan.md or test_report.md.

Explicitly unchanged (already on main via #806)

• Native update remains PATCH /fme/api/v4/feature-flags/{name} with Content-Type: application/merge-patch+json on routeResolver.headers.
• Native archive / unarchive remain POST …/archive and …/unarchive.
• Native kill / restore / reallocate remain aliases onto definition kill/restore/reallocate routes with environment_id as a query param.
• No new server.registerTool(). No fme_environment CRUD beyond list on this branch. No native fme_traffic_type / fme_workspace / fme_identity / fme_rollout_status on this branch (feat: wire native FME traffic type and rollout status lists #838 / feat: add native-only FME environment get, create, update, and delete #833 cover those).

Native create body (after this PR)

Field	Source	Notes
name	body.name or input.name	required — throws if missing
trafficType	body.trafficType | traffic_type_id | traffic_type | body.traffic_type	required — in the JSON body, never the path
description	body.description	optional
tags	body.tags	optional; strings wrapped as { name }
owners	body.owners	optional; { type: "USER", id | email } or { type: "GROUP", identifier }

Type of Change

• Bug fix (agent-facing create input + stale prompt)

Checklist

• Unit: tests/registry/feature-flags.test.ts + tests/registry/registry.test.ts
• No new public tools — registry bodyBuilder + prompt only

Coding Standards (registry-driven MCP model)

• No new server.registerTool() calls
• Existing feature-flags toolset
• No console.log() in src/

Test plan

• Native create with body.trafficType still matches the feat: [FME-17249]: FME dual-mode Harness-native scope migration #806 v4 body shape
• Native create with top-level traffic_type_id POSTs /fme/api/v4/feature-flags with { name, trafficType }
• Native create without name / without traffic type throws and does not call the client
• ResolvedRoute.headers win over spec.headers
• Live QA (optional): harness_create fme_feature_flag with org_id+project_id+traffic_type_id against QA

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[ravindraharness]

Closing as duplicate of the remaining product fix, which is now on #831 (c1c11b45).

Kept: native fme_feature_flag.create accepts traffic_type_id / traffic_type aliases and fails closed when name is missing.

Dropped from this PR:

• Prompt NYI rewrite — already handled on feat: wire native FME feature flag definition list, delete, and execute #831 / feat: wire native FME traffic type and rollout status lists #838 (this branch would have re-claimed rollout-status list as NYI).
• Generic ResolvedRoute.headers fixture — merge already shipped in feat: [FME-17249]: FME dual-mode Harness-native scope migration #806; not required for the create bug.