fix: skip false-positive fork detection after pickle in BQ analytics plugin

[caohy1988]

Summary

Fixes false-positive fork detection in the BigQuery Agent Analytics Plugin when deployed via Vertex AI Agent Engine (pickle/unpickle lifecycle).

Related: haiyuan-eng-google/BigQuery-Agent-Analytics-SDK#86 (Comcast production latency + fork warnings)

Problem

When the plugin is deployed via Agent Engine:

1. Plugin created locally → _init_pid = os.getpid()
2. Plugin pickled for deployment → __getstate__ sets _init_pid = 0
3. Plugin unpickled on server → _init_pid = 0
4. First request → _ensure_started() checks os.getpid() != self._init_pid
5. Since os.getpid() is never 0, this always evaluates to True
6. _reset_runtime_state() fires — tears down gRPC state, logs misleading "Fork detected (parent PID 0, child PID xx)" warning

No fork actually happened. The plugin was just unpickled. _started = False already ensures _lazy_setup() will run. The unnecessary _reset_runtime_state() adds cold-start latency and produces misleading log noise.

Fix

One-line change in _ensure_started():

# Before:
if os.getpid() != self._init_pid:

# After:
if self._init_pid != 0 and os.getpid() != self._init_pid:

This distinguishes:

• _init_pid == 0 → unpickled, never initialized in this process → skip reset
• _init_pid != 0 and _init_pid != os.getpid() → real fork from a different process → reset

Real forks are still caught by both:

• os.register_at_fork(after_in_child=_after_fork_in_child) (line 108)
• This PID check (for environments without register_at_fork)

Test plan

• 215 tests pass, 0 regressions
• test_no_reset_after_unpickle — unpickled plugin (_init_pid=0) does NOT trigger _reset_runtime_state
• test_reset_on_real_fork — plugin with a real non-zero _init_pid from a different process DOES trigger _reset_runtime_state

🤖 Generated with Claude Code

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[adk-bot]

Response from ADK Triaging Agent

Hello @caohy1988, thank you for creating this PR!

This PR is a bug fix. Per our contribution guidelines, could you please create a GitHub issue in this repository and associate it with this PR?

This will help us track the bug and the fix more effectively. Thanks!