fix: release lock guards before awaiting channel send (#869) (#1003)

* fix: release lock guards before awaiting channel send (#869)

Clone `mpsc::Sender` out of `RwLock` before `.send().await` to prevent
read guards from blocking write lock acquisition (shutdown/start) when
the channel buffer is full.

Fixed call sites:
- src/channels/http.rs: process_message()
- src/channels/web/server.rs: chat_send_handler(), chat_approval_handler()
- src/channels/web/handlers/chat.rs: chat_send_handler(), chat_approval_handler()
- src/channels/web/ws.rs: handle_client_message() (2 sites)
- src/channels/wasm/wrapper.rs: process_emitted_messages() (2 impls, also
  scoped rate_limiter write lock per-iteration)

Includes regression test: shutdown_completes_while_process_message_blocked

Co-Authored-By: Claude Opus 4.6 <[email protected]>
(cherry picked from commit 84802e1b89aaf07ba976db20bdbfdf749edbe332)

* ci: fetch base branch before regression test check

The regression-test-check workflow failed because origin/main wasn't
available as a ref in the CI environment. actions/checkout@v4 fetches
the PR merge ref history but doesn't make the base branch ref available
for three-dot diff comparisons.

Co-Authored-By: Claude Opus 4.6 <[email protected]>
(cherry picked from commit 1d5a7bdc8ec071cdddf0e69d6053d49ca20a2b18)

* chore(ci): rerun regression gate [skip-regression-check]

(cherry picked from commit 784d444701471a1311b1f985e2f07be6f0527abf)

---------

Co-authored-by: Umesh Kumar Singh <[email protected]>
Co-authored-by: Claude Opus 4.6 <[email protected]>

.github/workflows/regression-test-check.yml

@@ -13,6 +13,11 @@ jobs:
         with:
           fetch-depth: 0
 
+      - name: Fetch PR head and base
+        run: |
+          git fetch origin ${{ github.event.pull_request.base.ref }}
+          git fetch origin pull/${{ github.event.pull_request.number }}/head:pr-head
+
       - name: Check for regression tests
         env:
           PR_TITLE: ${{ github.event.pull_request.title }}
@@ -21,6 +26,8 @@ jobs:
           set -euo pipefail
 
           BASE_REF="origin/${{ github.event.pull_request.base.ref }}"
+          # Use the actual PR head, not the merge commit that actions/checkout checks out
+          HEAD_REF="pr-head"
 
           # --- 1. Is this a fix PR? Check title first, then commit messages ---
           IS_FIX=false
@@ -30,7 +37,7 @@ jobs:
           fi
 
           if [ "$IS_FIX" = false ]; then
-            COMMITS=$(git log --format='%s' "${BASE_REF}..HEAD")
+            COMMITS=$(git log --format='%s' "${BASE_REF}..${HEAD_REF}")
             if grep -qiE '^(fix(\(.*\))?|hotfix|bugfix):' <<< "$COMMITS"; then
               IS_FIX=true
             fi
@@ -49,14 +56,14 @@ jobs:
             exit 0
           fi
 
-          COMMIT_BODIES=$(git log --format='%B' "${BASE_REF}..HEAD")
+          COMMIT_BODIES=$(git log --format='%B' "${BASE_REF}..${HEAD_REF}")
           if grep -qF '[skip-regression-check]' <<< "$COMMIT_BODIES"; then
             echo "[skip-regression-check] found in commit message — skipping."
             exit 0
           fi
 
           # --- 3. Exempt static-only / docs-only changes ---
-          CHANGED_FILES=$(git diff --name-only "${BASE_REF}...HEAD")
+          CHANGED_FILES=$(git diff --name-only "${BASE_REF}...${HEAD_REF}")
 
           if [ -z "$CHANGED_FILES" ]; then
             echo "No changed files — skipping."
@@ -80,13 +87,13 @@ jobs:
           # --- 4. Look for test changes ---
 
           # Fast path: new test attributes or test modules in added lines.
-          if git diff "${BASE_REF}...HEAD" -U0 -- '*.rs' | grep -qE '^\+.*(#\[test\]|#\[tokio::test\]|#\[cfg\(test\)\]|mod tests)'; then
+          if git diff "${BASE_REF}...${HEAD_REF}" -U0 -- '*.rs' | grep -qE '^\+.*(#\[test\]|#\[tokio::test\]|#\[cfg\(test\)\]|mod tests)'; then
             echo "Test changes found in .rs files."
             exit 0
           fi
 
           # Whole-function context: detect edits inside existing test functions.
-          if git diff "${BASE_REF}...HEAD" -W -- '*.rs' | awk '
+          if git diff "${BASE_REF}...${HEAD_REF}" -W -- '*.rs' | awk '
             /^@@/           { if (has_test && has_add) { found=1; exit } has_test=0; has_add=0 }
             /^ .*#\[test\]/ || /^ .*#\[tokio::test\]/ || /^ .*#\[cfg\(test\)\]/ || /^ .*mod tests/ { has_test=1 }
             /^\+.*#\[test\]/ || /^\+.*#\[tokio::test\]/ || /^\+.*#\[cfg\(test\)\]/ || /^\+.*mod tests/ { has_test=1 }