Salesforce Hosted MCP — connector stays connected and tool list loads, but all tool invocations fail with "Unexpected error while invoking tool" (started 2026-08-21)

### MCP server URL or name

https://api.salesforce.com/platform/mcp/v1/platform/sobject-reads

### How are you connecting to this server?

From a custom connector URL I entered manually

### Where does the issue occur?

During a conversation (after initial auth)

### When did you last reproduce this?

2026-08-21 6:28 PM JST (09:28 UTC)

### Browser and OS

Claude Desktop app 1.34493.1 (Electron 42.9.2 / Node 24.18.1) on Windows (win32/x64)

### Describe the issue

The connector authorizes successfully and stays connected, but every tool invocation fails. This is a post-auth failure, distinct from the connect-time failures in #171, #184, #280 and #420 (all closed).

Current state:

- Connector shows as connected and is enabled in chat
- Tool list refresh succeeds, so the MCP session itself is alive
- Every tool invocation fails: tested `getUserInfo` and `getObjectSchema`, 3 attempts in the same session, no exceptions
- Disconnect and reconnect performed twice, no recovery

Timeline:

- Production connection was established successfully on 2026-08-07 and worked until 2026-08-20
- No Salesforce-side configuration changes since then
- First failure: 2026-08-21 15:50 JST (06:50 UTC); still failing at 18:28 JST (09:28 UTC)

Salesforce-side configuration (unchanged, verified):

- External Client App per the GA docs, callback `https://claude.ai/api/mcp/auth_callback`
- Scopes `mcp_api` and `refresh_token`
- "Issue JSON Web Token (JWT)-based access tokens for named users" enabled
- MCP server activated in Setup > API Catalog > MCP Servers
- Login history and OAuth usage logs record the authentication as successful
- A sandbox org with identical configuration works normally

### Error details

```shell
Unexpected error while invoking tool getUserInfo
Unexpected error while invoking tool getObjectSchema

Reference ID: ofid_bafbf07486a5b299
(note: this ofid was returned by an earlier connect-time auth error on the same
connector, before the token format was corrected on 2026-08-07. The current
tool-invocation failures do not surface a new ofid in the UI.)
```

### Expected behavior

Tool invocations should execute against the Salesforce MCP endpoint and return results, as they did between 2026-08-07 and 2026-08-20 with the same configuration.

### Additional context

Two other organizations reported the same symptom within hours on 2026-08-21, neither having changed any configuration. A related report from 2026-08-08 is included for context:

- #907 (comment, 2026-08-21 08:38 UTC) — same standard `sobject-reads` endpoint: OAuth completes, connector shows connected, tool definitions load, but `soqlQuery`, `find`, `listRecentSobjectRecords`, `getUserInfo` and `getObjectSchema` all fail with the same generic error. (The main body of #907 is a separate pre-auth discovery bug on a custom endpoint, which is why this is filed separately.)
- #782 (comment, 2026-08-21 04:51 UTC) — deployment stable since May with ~100 users, went down the same afternoon with "Unexpected error while invoking tool".
- #807 (open, 2026-08-08) — Cowork built-in Salesforce connector: write tools return the same error while reads keep working.

The simultaneity across orgs with no configuration changes on any side points to a client-side regression rather than per-org setup.

Also filed with Anthropic support (conversation ID available on request). Happy to provide additional trace IDs or run specific reproduction steps if that helps correlate logs.