WIP: Strip <think> blocks from chat responses (closes #73)

[strk-ai-agent]

Status: WIP / draft — do not merge.

Reasoning models that emit <think>...</think> inline in the regular
message stream (Qwen-style, DeepSeek R1, etc.) were leaking the raw
tags and reasoning content into every connector. This branch adds a
conservative stripThinkBlocks helper in src/session-utils.ts that
removes well-formed (closed) <think> blocks case-insensitively, and
applies it at the front of every connector's response cleaning
pipeline (matrix, slack, discord, mattermost, telegram, whatsapp, web).

Known issue — still leaking in some cases

Initial testing shows the stripper works for inline blocks that arrive
entirely on the agent_message_chunk channel, but occasionally an
orphan </think> tag still reaches the chat. The current regex
(/<think>[\s\S]*?<\/think>/gi) requires both tags in the same string,
so it misses blocks split across the two ACP channels — most likely
when the model emits the opening <think> on agent_thought_chunk
(which the connectors drop into updateHandler rather than
responseBuffer) and the closing </think> plus the answer on
agent_message_chunk. With only the closing half in
responseBuffer, the helper has nothing to match and the orphan
</think> survives cleaning.

I am still debugging this. Likely next steps:

1. Add a one-shot debug log of the raw responseBuffer (and any
   agent_thought_chunk text captured separately) on the affected
   connector to confirm the channel-split hypothesis.
2. Either widen the regex to also strip orphan </think> (with a
   warning, dropping the conservative guarantee) or capture
   agent_thought_chunk text into the same buffer so the regex sees
   both halves.
3. Re-run and confirm no <think> / </think> survives on any
   connector before removing the WIP/draft flag.

Tracking issue: #73.

[ominiverdi]

Closing under the updated contribution policy. The current submission volume and required verification exceed this project’s review capacity, and pull requests from autonomous or delegated agent accounts are no longer accepted. Valid underlying issues may remain open for independent implementation. Please do not revise, reopen, or replace this pull request.

[ominiverdi]

@strk: please stop submitting implementation pull requests through strk-ai-agent. Future contributions must be reviewed, understood, and submitted by a human; discussed with a maintainer before implementation where required; and limited to one active implementation pull request at a time. Resubmitting the closed work through another account would circumvent this boundary. Valid bug reports can remain open. This is a final maintainer-capacity decision, not a request to revise the current backlog.