feat(mcp): add OAuth authentication

[sam-saffron-jarvis]

Summary

• upgrade github.com/modelcontextprotocol/go-sdk from v1.5.0 to the latest stable v1.7.0
• add persistent OAuth authorization for remote Streamable HTTP MCP servers using the SDK's InitialTokenSource and NewTokenSource hooks
• add first-class login, status, refresh, reauthentication, cancellation, revocation, and logout workflows across CLI, chat TUI, and Web UI
• keep stdio, unauthenticated HTTP, and explicit static Authorization headers backward-compatible

OAuth and credential handling

• MCP protected-resource and authorization-server discovery
• PKCE, dynamic client registration, issuer binding, resource indicators, scope accumulation, and refresh-token guidance through go-sdk v1.7.0
• versioned private credential file with 0700 directory / 0600 file permissions, symlink rejection, atomic writes, and cross-process locking
• rotating refresh-token adoption and stale-write protection across processes
• RFC 7009 revocation where advertised
• no tokens, authorization codes, verifiers, or client secrets in web JSON, browser storage, transcripts, or logs

UX

CLI

term-llm mcp login <server>
term-llm mcp status [server]
term-llm mcp logout <server>

Includes --force, --no-browser, and --local-only variants.

TUI

• signed-out, waiting, signed-in, transient-error, and reauthentication states
• /mcp login and /mcp logout
• successful authorization reconnects only the affected server

Web

• Sign in / Sign in again / Retry / Cancel / Copy link / Sign out actions
• popup plus polling/postMessage completion
• state-gated callback that never reflects query data
• serve --public-url / TERM_LLM_SERVE_PUBLIC_URL for externally visible OAuth callbacks

Review findings incorporated

A claude-bin:fable implementation review found and fixed four issues before publication:

1. custom MCP headers could leak to authorization-server requests
2. a stored DCR client could be reused with an incompatible redirect URI
3. a hung refresh endpoint could hold the cross-process store lock indefinitely
4. the Web UI could poll a flow forever after it disappeared server-side

Each fix has regression coverage.

Validation

• go test ./internal/mcp/... ./internal/tui/chat ./internal/serveui
• isolated go test ./cmd
• go test -race ./internal/mcp/oauth ./internal/mcp
• go vet ./...
• go build ./...
• frontend format, ESLint, Stylelint, and TypeScript checks
• frontend tests: 425 passed across 33 files
• live Linear OAuth smoke: browser consent, persisted restart reuse, read write scopes, and 57 tools discovered
• live CLI and web grants were revoked after the smoke test

[SamSaffron]

merged by hand