feat(mcp): add MCP tool surface for the full X client API

[teslashibe]

Summary

Adds a new ./mcp subpackage built on github.com/teslashibe/mcptool v0.1.0 that exposes every exported *x.Client method as an MCP tool with a typed input struct. Each tool's JSON input schema is reflected from struct tags, so there is no hand-maintained schema and no drift between this package's API and what an agent sees.

The structure mirrors linkedin-go/mcp (just merged via teslashibe/linkedin-go#9): one Provider, one tool-group file per logical area, one shared Excluded map of intentional non-exposures with reasons.

Tools (37)

Reads (19)

• Profile / identity: x_get_profile, x_get_profile_by_id, x_me
• Social graph: x_get_followers, x_get_following
• Tweets: x_get_tweet, x_get_tweet_detail, x_get_user_tweets
• Timelines: x_home_timeline, x_home_latest_timeline
• Search: x_search_tweets, x_search_users, x_advanced_search_tweets
• DMs: x_get_conversations, x_get_conversation
• Lists: x_get_list, x_get_list_timeline, x_get_list_members
• Analysis: x_scrape_timeline_trends

Writes (18)

• Compose: x_create_tweet, x_reply, x_quote_tweet, x_delete_tweet
• Engagement: x_like, x_unlike, x_retweet, x_unretweet, x_bookmark, x_unbookmark
• Social: x_follow, x_unfollow, x_mute, x_unmute, x_block, x_unblock
• DM: x_send_dm, x_send_new_dm

All tools use snake_case x_<verb>_<noun> names and have descriptions ≤ 120 chars (enforced by TestToolsValidate). List-returning tools use mcptool.PageOf so the host's response middleware can uniformly cap and surface next_cursor. Write tools return { "ok": true, ...key fields... } on success.

Excluded (13)

Internal / lifecycle helpers — surfaced via the host application's middleware, not as agent-callable tools:

Method	Reason
RateLimit	observability surfaced via the host's MCP middleware
TransactionInitErr	bootstrap state reported at construction
RefreshQueryIDs	internal session-bootstrap helper

Convenience wrappers around the corresponding *Page variant — exposed as a single cursor-aware tool to keep the surface compact while retaining pagination:

HomeTimeline, HomeLatestTimeline, UserTweets, SearchTweets, SearchUsers, AdvancedSearchTweets, GetFollowers, GetFollowing, GetListTimeline, GetListMembers.

Drift prevention

mcp/mcp_test.go runs mcptool.Coverage(reflect.TypeOf(&x.Client{}), Provider{}.Tools(), Excluded) and fails when:

• an exported method on *x.Client is neither wrapped by a tool nor listed in Excluded (Missing)
• Excluded references a method that no longer exists (UnknownExclusions)

Current report: 37 wrapped, 13 excluded, 0 missing, 0 unknown exclusions.

Tools also pass mcptool.ValidateTools (canonical name regex, ≤ 120-char description, non-nil Invoke and InputSchema, no duplicates) and the x_ prefix check.

CI

Adds .github/workflows/mcp-ci.yml. On any push to main or PR touching mcp/**, **/*.go, go.mod, go.sum, or the workflow itself:

1. go mod tidy — must produce no diff
2. go vet ./...
3. go build ./...
4. go test -race -count=1 ./mcp/...

Guardrails respected

• No changes to existing tests or non-MCP code
• Go toolchain version in go.mod unchanged (1.25.5)
• Only new dependency: github.com/teslashibe/mcptool v0.1.0 (and its transitive deps)
• All write methods are exposed (no policy gating in the package — that's the host's job)

Test plan

• go vet ./... clean
• go build ./... clean
• go test -race -count=1 ./mcp/... green locally
• Coverage test reports 0 missing, 0 unknown exclusions
• All 37 tool names validate; descriptions ≤ 120 chars; x_ prefix
• CI green on this PR

Refs: teslashibe/agent-setup#6