fix(sessions): heal stale profile schemas on read

[Tilly-YL]

What does this PR do?

Hermes Desktop reads every profile's state.db in read-only mode when it builds the session list. Read-only opens skip schema reconciliation. The existing probe checked four named columns, so an older profile without sessions.last_read_at passed the probe and failed later with no such column: s.last_read_at. The cross-profile list and batched sidebar routes also opened SessionDB directly. They caught that failure and returned an empty list, which made intact sessions appear missing after an update or restart.

This change derives cached LIMIT 0 probes from every table and column declared in SCHEMA_SQL. A current database remains read-only. A stale profile follows the existing one-time writable reconciliation path and is reopened read-only. Both cross-profile session routes now use that shared helper.

Related Issue

Fixes #79531

This follows the direction introduced in #42487. The commit retains liuhao1024's credit and extends the fix to the current shared helper and the Desktop sidebar route. The reproduction and schema analysis from wangyi0177-eng in #79531 helped isolate the last_read_at case.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Security fix
• Documentation update
• Tests (adding or improving test coverage)
• Refactor (no behavior change)
• New skill (bundled or hub)

Changes Made

hermes_cli/web_server.py now builds the read-only probes from SCHEMA_SQL and uses the existing writable reconciliation path when any declared table or column is missing.

hermes_cli/web_routers/profiles.py now routes both /api/profiles/sessions and /api/profiles/sessions/sidebar through _open_session_db_for_profile.

tests/hermes_cli/test_web_server.py covers missing last_read_at and profile_name columns, plus both cross-profile session endpoints.

How to Test

1. Create a named profile database with the current SessionDB, add one session and one message, then remove sessions.last_read_at to model a database created before that column was added.
2. Request /api/sessions, /api/profiles/sessions, and /api/profiles/sessions/sidebar. Each route should return the existing session, and PRAGMA table_info(sessions) should show that last_read_at was restored.
3. Run the focused test and compatibility commands listed below.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes
• I've tested on macOS 26.5.2

Documentation & Housekeeping

• Relevant documentation is unchanged; docstrings were updated where behavior changed
• No config keys were added or changed
• No contributor workflow or architecture document changed
• I considered Windows and macOS compatibility
• No tool descriptions or schemas changed

Screenshots / Logs

python -m pytest tests/hermes_cli/test_web_server.py -q
143 passed

python -m pytest tests/hermes_cli/test_dashboard_param_clamps.py -q
9 passed

python -m pytest tests/test_web_server_sessiondb_eventloop.py -q
3 passed

python scripts/check-windows-footguns.py --all
No Windows footguns found (917 files scanned)

git diff --check origin/main...HEAD
clean

I also started scripts/run_tests.sh. At 28.8%, the runner had reported 7,630 passing checks and 12 failures, so I stopped the run. The failures were outside the modified files and came from missing optional SDKs, the live-system signal guard, credential-routing expectations, and a network isolation test. The focused web server tests above all pass on the rebased commit.

[jquesnelle]

Appreciate the contribution! Closed by #80797