Add goal persistence foundation (1 / 5) (#18073)

Adds the persisted goal foundation for the rest of the stack. This PR is
intentionally limited to feature flag and state-layer behavior;
app-server APIs, model tools, runtime continuation, and TUI UX are
layered in later PRs.

## Why

Goal mode needs durable thread-level state before clients or model tools
can safely build on it. The state layer needs to know whether a goal
exists, what objective it tracks, whether it is active, paused,
budget-limited, or complete, and how much time/token usage has already
been accounted.

## What changed

- Added the `goals` feature flag and generated config schema entry.
- Added the `thread_goals` state table and Rust model for persisted
thread goals.
- Added state runtime APIs for creating, replacing, updating, deleting,
and accounting goal usage.
- Added `goal_id`-based stale update protection so an old goal update
cannot overwrite a replacement.
- Kept this PR scoped to persistence and state runtime behavior, with no
app-server, model-facing, continuation, or TUI behavior yet.

## Verification

- Added state runtime coverage for goal creation, replacement, stale
update protection, status transitions, token-budget behavior, and usage
accounting.

codex-rs/state/src/model/mod.rs

@@ -3,6 +3,7 @@ mod backfill_state;
 mod graph;
 mod log;
 mod memories;
+mod thread_goal;
 mod thread_metadata;
 
 pub use agent_job::AgentJob;
@@ -25,6 +26,8 @@ pub use memories::Stage1JobClaimOutcome;
 pub use memories::Stage1Output;
 pub use memories::Stage1OutputRef;
 pub use memories::Stage1StartupClaimParams;
+pub use thread_goal::ThreadGoal;
+pub use thread_goal::ThreadGoalStatus;
 pub use thread_metadata::Anchor;
 pub use thread_metadata::BackfillStats;
 pub use thread_metadata::ExtractionOutcome;
@@ -38,6 +41,7 @@ pub(crate) use agent_job::AgentJobItemRow;
 pub(crate) use agent_job::AgentJobRow;
 pub(crate) use memories::Stage1OutputRow;
 pub(crate) use memories::stage1_output_ref_from_parts;
+pub(crate) use thread_goal::ThreadGoalRow;
 pub(crate) use thread_metadata::ThreadRow;
 pub(crate) use thread_metadata::anchor_from_item;
 pub(crate) use thread_metadata::datetime_to_epoch_millis;

codex-rs/state/src/model/thread_goal.rs

@@ -0,0 +1,109 @@
+use anyhow::Result;
+use anyhow::anyhow;
+use chrono::DateTime;
+use chrono::Utc;
+use codex_protocol::ThreadId;
+use sqlx::Row;
+use sqlx::sqlite::SqliteRow;
+
+use super::epoch_millis_to_datetime;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ThreadGoalStatus {
+    Active,
+    Paused,
+    BudgetLimited,
+    Complete,
+}
+
+impl ThreadGoalStatus {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::Active => "active",
+            Self::Paused => "paused",
+            Self::BudgetLimited => "budget_limited",
+            Self::Complete => "complete",
+        }
+    }
+
+    pub fn is_active(self) -> bool {
+        self == Self::Active
+    }
+
+    pub fn is_terminal(self) -> bool {
+        matches!(self, Self::BudgetLimited | Self::Complete)
+    }
+}
+
+impl TryFrom<&str> for ThreadGoalStatus {
+    type Error = anyhow::Error;
+
+    fn try_from(value: &str) -> Result<Self> {
+        match value {
+            "active" => Ok(Self::Active),
+            "paused" => Ok(Self::Paused),
+            "budget_limited" => Ok(Self::BudgetLimited),
+            "complete" => Ok(Self::Complete),
+            other => Err(anyhow!("unknown thread goal status `{other}`")),
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ThreadGoal {
+    pub thread_id: ThreadId,
+    pub goal_id: String,
+    pub objective: String,
+    pub status: ThreadGoalStatus,
+    pub token_budget: Option<i64>,
+    pub tokens_used: i64,
+    pub time_used_seconds: i64,
+    pub created_at: DateTime<Utc>,
+    pub updated_at: DateTime<Utc>,
+}
+
+pub(crate) struct ThreadGoalRow {
+    pub thread_id: String,
+    pub goal_id: String,
+    pub objective: String,
+    pub status: String,
+    pub token_budget: Option<i64>,
+    pub tokens_used: i64,
+    pub time_used_seconds: i64,
+    pub created_at_ms: i64,
+    pub updated_at_ms: i64,
+}
+
+impl ThreadGoalRow {
+    pub(crate) fn try_from_row(row: &SqliteRow) -> Result<Self> {
+        Ok(Self {
+            thread_id: row.try_get("thread_id")?,
+            goal_id: row.try_get("goal_id")?,
+            objective: row.try_get("objective")?,
+            status: row.try_get("status")?,
+            token_budget: row.try_get("token_budget")?,
+            tokens_used: row.try_get("tokens_used")?,
+            time_used_seconds: row.try_get("time_used_seconds")?,
+            created_at_ms: row.try_get("created_at_ms")?,
+            updated_at_ms: row.try_get("updated_at_ms")?,
+        })
+    }
+}
+
+impl TryFrom<ThreadGoalRow> for ThreadGoal {
+    type Error = anyhow::Error;
+
+    fn try_from(row: ThreadGoalRow) -> Result<Self> {
+        Ok(Self {
+            thread_id: ThreadId::try_from(row.thread_id)?,
+            goal_id: row.goal_id,
+            objective: row.objective,
+            status: ThreadGoalStatus::try_from(row.status.as_str())?,
+            token_budget: row.token_budget,
+            tokens_used: row.tokens_used,
+            time_used_seconds: row.time_used_seconds,
+            created_at: epoch_millis_to_datetime(row.created_at_ms)?,
+            updated_at: epoch_millis_to_datetime(row.updated_at_ms)?,
+        })
+    }
+}