bug(adapters/slack): HistoryReader fails on live Slack — conversations.history/replies sent as JSON #98

The Slack adapter's HistoryReader does not work against live Slack. The Slack adapter is supported tier.

What happens

ReadHistory in adapters/slack/history.go sends conversations.history and conversations.replies through the adapter's shared call path. That path serializes the payload as a JSON body (slack.go ~L684–693, Content-Type: application/json). Slack's conversations.* read methods do not accept JSON arguments. Live Slack answers HTTP 200 with invalid_arguments (missing required field: channel).

The unit and hardening tests pass because the fake server accepts JSON. Only a live workspace shows the failure. It was found by the env-gated TestLive in #97.

Impact

Every history read on live Slack fails, for both thread replies and DM history.

Fix

#97 is the proposed fix: its slackapi client sends these methods form-encoded. When the fix lands, the tests should assert the actual form parameters and pagination for both endpoints, so a permissive fake cannot hide the problem again. If #97 needs a longer design cycle, the maintainer will coordinate extracting a small standalone fix, so the supported adapter doesn't stay broken.

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