fix(ai): MCP bridge dropped the API path prefix on relative URLs#348
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The bridge built relative request URLs with a LEADING slash (/search,
/me/highlights/{id}, /books/{id}/ask, /auth/device/*) and set
HttpClient.BaseAddress WITHOUT a trailing slash. When TEXTSTACK_API_URL
carries a path prefix (e.g. https://textstack.app/api), .NET resolves a
leading-slash relative URI from the host ROOT and drops the prefix → the
bridge hit https://textstack.app/search (the SPA, 301→HTML) instead of
.../api/search → JsonException → 'upstream unavailable'.
Silently fine in unit tests (fake handler ignores BaseAddress) and in the
prod-internal deployment (TEXTSTACK_API_URL=http://api:8080, no prefix) —
surfaced only when dogfooding Claude Desktop against the public /api host.
Fix: McpBridgeCore.BaseUri() trailing-slash-normalizes the base; the API
client's Relative() strips the leading slash on every relative URI; the
device-flow client + its 3 URLs get the same treatment. 9 regression
tests assert the resolved ABSOLUTE RequestUri preserves the /api prefix
(verified 7/9 fail without the fix). 629 unit green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Bug — MCP bridge dropped the
/apiprefix (caught while dogfooding)Building the local MCP server and pointing it at the public API (
TEXTSTACK_API_URL=https://textstack.app/api), every tool failed with"... failed: upstream unavailable".Root cause: the bridge's
TextStackApiClientbuilt relative request URLs with a leading slash (/search,/me/highlights/{id},/books/{id}/ask,/auth/device/*) whileHttpClient.BaseAddresshad no trailing slash. .NET resolves a leading-slash relative URI from the host root, dropping the/apiprefix → the bridge hithttps://textstack.app/search(the SPA →301/HTML) instead ofhttps://textstack.app/api/search→JsonException→ the clean "upstream unavailable" IsError.Why it hid: unit tests use a fake
HttpMessageHandlerthat ignoresBaseAddress, and the prod Docker deployment setsTEXTSTACK_API_URL=http://api:8080(no path prefix), so the dropped-prefix never bit. It only surfaces against a prefixed base URL — exactly the local-dogfood / any reverse-proxied/apicase.Fix
McpBridgeCore.BaseUri(apiBaseUrl)— trailing-slash-normalizes the base so the prefix segment isn't treated as a file and replaced. Used by both the typedTextStackApiClientand the device-flow named client.TextStackApiClient.Relative(url)— strips the leading slash on every relative request URI (PublicRequest+AuthorizedRequestAsync).DeviceFlowTokenProvider— its 3 URLs (auth/device/code,auth/device/token,auth/refresh-mobile) lose their leading slash too.Verified live: after the fix,
search_booksagainst prod returns real results (Dracula/ Bram Stoker).Regression test —
tests/TextStack.UnitTests/McpApiPrefixTests.cs(9)A capturing handler wired through the real
TextStackApiClientwith a prefixedBaseAddress(http://localhost/api/) asserts the resolved absoluteRequestUripreserves the prefix:search_books→http://localhost/api/search?...list_my_highlights→http://localhost/api/me/highlights/{id}ask_book→http://localhost/api/books/{id}/askhttp://localhost/api/auth/device/codeBaseUrihelper: appends one trailing slash, idempotent.Proven to catch the bug: temporarily reverting the fix makes 7/9 fail with the exact signature (
http://localhost/me/highlights/...vs expected.../api/...).Verify
dotnet test tests/TextStack.UnitTests→ 629 pass (+9); existing MCP tests + StudyBuddy set-equality greendotnet build/dotnet format(whitespace+style) → clean🤖 Generated with Claude Code