[Repo Assist] feat(envutil): add GetEnvDuration + configurable MCP_GATEWAY_SESSION_TIMEOUT

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Summary

Adds GetEnvDuration to internal/envutil (consistent with existing GetEnvString/GetEnvInt/GetEnvBool), and uses it to make the unified-mode MCP session timeout configurable via the MCP_GATEWAY_SESSION_TIMEOUT environment variable.

Motivation

The session timeout in server/transport.go was hardcoded at 2 hours with a comment "2h accommodates long-running workflows with idle periods". While the default is good, operators may need to:

• Shorten it for tighter security postures or faster-cycling workflows
• Lengthen it for unusually long-running agentic sessions

This was identified as a best-practice alignment item in the go-sdk module review (#3054).

Changes

internal/envutil/envutil.go

// GetEnvDuration returns the time.Duration value of the environment variable specified by envKey.
// If the environment variable is not set, is empty, or cannot be parsed by time.ParseDuration,
// it returns the defaultValue. Accepts any string valid for time.ParseDuration (e.g. "2h", "30m", "90s").
func GetEnvDuration(envKey string, defaultValue time.Duration) time.Duration {
    if envValue := os.Getenv(envKey); envValue != "" {
        if d, err := time.ParseDuration(envValue); err == nil && d > 0 {
            return d
        }
    }
    return defaultValue
}

internal/server/transport.go

SessionTimeout: envutil.GetEnvDuration("MCP_GATEWAY_SESSION_TIMEOUT", 2*time.Hour),

internal/envutil/envutil_test.go

9 table-driven test cases covering: valid durations ("2h", "30m", "90s", "1h30m"), missing env var, empty string, invalid string, zero duration, and negative duration. Plus a real-world scenario test for MCP_GATEWAY_SESSION_TIMEOUT.

Usage

# Shorten session timeout to 30 minutes
MCP_GATEWAY_SESSION_TIMEOUT=30m ./awmg --config config.toml

# Extend to 4 hours for long-running workflows
MCP_GATEWAY_SESSION_TIMEOUT=4h ./awmg --config config.toml

# Default (2h) - no change in behavior if env var is unset
./awmg --config config.toml

Invalid, zero, or negative values fall back to the 2h default silently.

Test Status

⚠️ Infrastructure limitation: The CI build environment cannot download Go modules (network proxy access is blocked), so make agent-finished could not be run. The changes are:

• Syntactically valid (gofmt clean on all changed files)
• The GetEnvDuration implementation follows the identical pattern as GetEnvInt (which is well-tested and in production use)
• Tests are table-driven and follow the same structure as existing envutil tests

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[Copilot]

Pull request overview

Adds a new environment helper to parse time.Duration values and uses it to make the MCP Streamable HTTP session timeout configurable via MCP_GATEWAY_SESSION_TIMEOUT (default remains 2h).

Changes:

• Add envutil.GetEnvDuration (patterned after existing envutil helpers).
• Wire MCP_GATEWAY_SESSION_TIMEOUT into sdk.StreamableHTTPOptions.SessionTimeout.
• Add table-driven unit tests for duration parsing and fallback behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
internal/envutil/envutil.go	Introduces GetEnvDuration for parsing positive durations from env vars.
internal/server/transport.go	Uses GetEnvDuration to configure MCP session timeout via MCP_GATEWAY_SESSION_TIMEOUT.
internal/envutil/envutil_test.go	Adds unit tests covering valid/invalid duration env values and a session-timeout scenario.

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[Copilot]

The docstring says this falls back only when the env var is unset/empty or cannot be parsed, but the implementation also falls back when the parsed duration is non-positive (d <= 0). Please update the comment to mention the > 0 requirement (similar to GetEnvInt) so behavior and docs match.

[Copilot]

Tests are manually setting/unsetting environment variables via os.Unsetenv/os.Setenv. The repo frequently uses testing.T.Setenv for this (e.g., internal/sys/container_test.go:12-68), which automatically restores env vars via t.Cleanup and is safer if tests ever become parallelized. Consider switching these cases to t.Setenv (and avoiding manual Unsetenv/defer).