[gilalon-pplx]

Summary

Record the optional guest Ping reading as the sandbox.guest.mem_used_bytes distribution, tagged with template, alongside the existing guest-spec metrics. Cache the template name with the watchdog's existing sandbox metadata so recording a sample adds no database query or template lookup.

Carry the reading alongside health observations and emit it only when the watchdog accepts a probe of a Started sandbox. The lifecycle-epoch fence rejects stale results, removed sandboxes contribute nothing, and missing readings are neither cached nor replayed. Memory usage does not change health status.

Paused sandboxes, including normally paused ready warm-pool slots, are not pinged and record nothing. This is a lifecycle filter, not a pool-membership filter: a pool-marked sandbox that is actually Started can contribute, without a separate pool tag. Samples arrive on the existing probe schedule, approximately every 25–40 seconds including scheduler rounding, and count observations rather than distinct sandboxes.

Validation

Head: a3d33be05c253942fc57036bd8650a8abc66b1f6, directly based on #1668 head 5de789f85; both contain main 3a6e89f3b.

• Local validation on combined stack head ded1ef354: cargo test --locked -p pplx-space-sbx-mgr --lib watchdog:: passed all 55 tests. The existing lifecycle_edge_preserves_status_and_discards_in_flight_probe covers stale-probe rejection; telemetry-only population tests are not added.
• Formatting and strict all-target/all-feature Clippy passed locally for sandbox-manager, guest-server, and host-server.
• The metric feature diff is unchanged by this restack. Backend delivery is exercised by local.telemetry_reaches_local_backends in the dependent #1670 new-head CI run, currently pending completion.

The combined stack also passed the full Python CI runner: generated-index validation and 1,931 tests without skips.

Severity and risk

Severity does not apply: this adds observability rather than fixing an incident. Risks include incorrect sample attribution or population and additional metric-series cardinality from template names. Deployment dimensions come from the sink; no sandbox ID or client ID is added explicitly.

Guest readings are tenant-controlled and are not bounded against trusted configured memory. They are used-memory observations, not a utilization ratio, enforcement signal, or trusted accounting. Older guests can omit the field without changing health behavior. Reverting stops emission.

Stack

Part 2 of 3, based on guest reporting (#1668). Merge that PR first, this metric second, and telemetry delivery smoke (#1670) last. Each PR contains one focused commit with a final-behavior commit message.

AI assistance: Perplexity assisted with code, tests, review, and this description.

[coderabbitai]

No actionable comments were generated in the recent review.

Walkthrough

The watchdog now carries the sandbox template and optional guest-memory reading through health probes. It records a template-tagged distribution when an accepted probe has a reading and the sandbox is Started. The guest-memory metric and its sampling conditions are documented. Tests update probe fixtures to include the template and optional memory fields.

Merge Risk: Moderate · up to a3d33

This change adds a guest memory metric tagged by sandbox template to the watchdog's health probes. It should not affect sandbox health or lifecycle, but nothing in the PR tests that samples are attributed to the right sandbox state or template. The Kind end-to-end run was on a different head, and the PR's own Kind job was skipped. Confirm that evidence or add population tests before merging; reverting the change stops emission.

Security architecture risk: Minimal · up to 7801e

The inspected change adds optional memory telemetry without granting privileges or using guest-reported values for enforcement. Existing probe acceptance checks also gate the new samples. No introduced material security or failure-containment risk was established.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — A guest capable of falsifying Ping responses can influence memory observations attributed to its sandbox's template and therefore that template's aggregate distribution. The inspected path does not let the response choose the template label, attach a sandbox identifier, or acquire lifecycle authority.

Trust Boundaries and Controls

• observed — The existing guest probe requires runtime PID and UID metadata, requests the corresponding expected Unix-socket peer, applies a response decoding limit, and runs within a 500 ms timeout. The PR reads memory from this existing successful response path rather than adding a new guest connection or credential capability.

Resilience and Maintainability Implications

• observed — The pre-existing guest memory reader waits at most 100 ms and uses non-waiting semaphore admission. Its blocking worker retains the permit after RPC cancellation or timeout until the read finishes, preventing replacement requests from bypassing that admission control. Unavailable memory does not fail Ping.

Pre-merge checks: 6

Check name	Status	Explanation
Title check		The title starts with the lowercase area "sbx-mgr:" followed by a lowercase summary word, has no trailing period, no ticket ID, and no internal links. It names the main change: emitting template-tagge…
Description Follows The Pr Template		The PR description contains all four required items, each with real content. 1. "## Summary" section: Present. It states that merging records the optional guest Ping reading as the `sandbox.guest.…
Bug Fixes Name A Regression Test		The check applies only when the PR fixes a defect in application behavior under crates/, shim/, or ui/. This PR adds a new observability feature, not a bug fix. Evidence from the provided PR metadata:…
Weakened Safeguards Are Justified		The PR changes six files: guest_bridge.rs, service/tests.rs, watchdog.rs, watchdog/diagnostics/tests.rs, watchdog/tests.rs, and docs/observability.md. I checked the full diff against the reviewed base…
Agent Tooling Runs No New Commands		The check is inapplicable to this PR, so it passes. The diff range changes six files: five Rust sources under crates/l40_api/sbx/mgr/server/src/ (metrics/sandbox/worker/guest_bridge.rs, `service/t…
Public-Safe Content		The diff, title, and description contain none of the content the Public-safe content check prohibits. - Scope: six files changed. Five are Rust sources and tests; one is docs/observability.md. - Pat…

Full details: Title check

Explanation

The title starts with the lowercase area "sbx-mgr:" followed by a lowercase summary word, has no trailing period, no ticket ID, and no internal links. It names the main change: emitting template-tagged guest memory samples from the watchdog, which matches the raw summary and the PR objectives. The code identifier casing is preserved in the body and the title meets every stated format rule.

Full details: Description Follows The Pr Template

Explanation

The PR description contains all four required items, each with real content. 1. "## Summary" section: Present. It states that merging records the optional guest Ping reading as the sandbox.guest.mem_used_bytes distribution, tagged with template, and that the watchdog emits it only for accepted probes of Started sandboxes. 2. "## Validation" section: Present. It names what was run and the result: cargo test --locked -p pplx-space-sbx-mgr --lib watchdog:: passed all 55 tests, formatting and strict Clippy passed, and the Python CI runner passed with 1,931 tests. It also names the pending #1670 CI run. 3. "## Severity and risk" section: Present. It gives a severity ("Severity does not apply: this adds observability rather than fixing an incident") and lists risks (incorrect sample attribution or population, metric-series cardinality from template names, tenant-controlled readings). 4. "AI assistance:" line: Present. It reads "AI assistance: Perplexity assisted with code, tests, review, and this description." This check judges presence only, so no content quality or length was assessed. No tool calls were needed because the check depends only on the description text.

Full details: Bug Fixes Name A Regression Test

Explanation

The check applies only when the PR fixes a defect in application behavior under crates/, shim/, or ui/. This PR adds a new observability feature, not a bug fix. Evidence from the provided PR metadata: - Title: "sbx-mgr: emit template-tagged guest memory samples from the watchdog." - Description: records the optional guest Ping reading as a new sandbox.guest.mem_used_bytes distribution. It states "Severity does not apply: this adds observability rather than fixing an incident." - Raw summary: adds a public guest_memory_used function, a new SidecarInfo::template field, and a memory_used_bytes field on the probe result. It also adds a docs section. These are new capabilities. - The other changes (test fixture updates and the returned transition in apply_guest_outcome) support the new feature. The summary does not describe a defect correction. Because the PR is not an application bug fix, the check passes. I did not inspect the diff directly. This verdict relies on the PR title, description, and raw summary.

Full details: Weakened Safeguards Are Justified

Explanation

The PR changes six files: guest_bridge.rs, service/tests.rs, watchdog.rs, watchdog/diagnostics/tests.rs, watchdog/tests.rs, and docs/observability.md. I checked the full diff against the reviewed base for each item in the custom check. - Removed tests or assertions: None. Every removed line is production code in watchdog.rs, for example the health_observation(...) call sites and the apply_composed_health_result return path. The test-file hunks add only fixture fields (template: "seed", memory_used_bytes: None). In diagnostics/tests.rs, apply_guest_outcome gains .and_then(|accepted| accepted.transition). This adapts the helper to the new return type and does not drop an assertion. - Lint or allow attributes: No #[allow(...)], #[expect(...)], #[ignore], skip, or xfail was added. - Allowlists, baselines, and CI: No change to deny.toml, clippy.toml, nextest config, CI workflows, continue-on-error, SPACE_TEST_DEPS_OPTIONAL, Cargo [lints] tables, or ci/kind-pull-paths.txt. - Review-guidance files: No change to AGENTS.md, CLAUDE.md, .agents/, CONTRIBUTING.md, or docs/rust/. The only documentation change is docs/observability.md, which is not one of the listed guidance files. Its text describes the metric and does not address review, merge-risk, or approval handling. The custom check fails only on weakened safeguards or review-steering text in those files. None were found, so the check passes.

Full details: Agent Tooling Runs No New Commands

Explanation

The check is inapplicable to this PR, so it passes. The diff range changes six files: five Rust sources under crates/l40_api/sbx/mgr/server/src/ (metrics/sandbox/worker/guest_bridge.rs, service/tests.rs, watchdog.rs, watchdog/diagnostics/tests.rs, watchdog/tests.rs) and docs/observability.md. None of these is a plugin manifest (plugin.json/plugin.yaml), a SKILL.md, a skill or command file, an MCP/LSP config, or an agent guideline file (AGENTS.md, CLAUDE.md). A path search for those names returned no matches. A search of the added diff lines for inline shell substitution (! followed by a backtick), hooks, allowed-tools, mcpServers, lspServers, or command: also returned no matches. docs/observability.md adds an observability reference section. It is not an agent-read guideline file, and its added text contains no command or server entry. No agent-run content is introduced.

Full details: Public-Safe Content

Explanation

The diff, title, and description contain none of the content the Public-safe content check prohibits. - Scope: six files changed. Five are Rust sources and tests; one is docs/observability.md. - Pattern scan: I searched all added lines for URLs, /Users/ and /home/ paths, AWS ARNs, 12-digit account IDs, secret and token keywords, private-key headers, internal or private-domain hostnames, private IP ranges, and chat or tracker names. No matches. - Literal scan: I searched the Rust additions for long token-like strings, 40-character hex strings, email addresses, and long numeric literals. None found. - Docs and doc comments: the new docs/observability.md section and the guest_memory_used doc comment describe the metric in general terms. They name no real cluster or environment, and they contain no production logs or measurements. - Description: it links only to public GitHub pull requests and a public Actions run. It cites commit hashes and a test count. These are not sensitive. - Test fixtures: the values are placeholders such as "seed" and None. No security vulnerability is described. No incident details appear.

Recent review info

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Commit: a3d33be05c25.

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Reviewing files that changed from the base of the PR and between f4b2dba and 826fbdb.

Files selected for processing: 5

• crates/l40_api/sbx/mgr/server/src/metrics/sandbox/worker/guest_bridge.rs
• crates/l40_api/sbx/mgr/server/src/service/tests.rs
• crates/l40_api/sbx/mgr/server/src/watchdog.rs
• crates/l40_api/sbx/mgr/server/src/watchdog/tests.rs
• docs/observability.md

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[ac-pplx]

The problem. #1668 makes the Linux guest report its used memory (MemTotal - MemAvailable) on the watchdog's health Ping, but nothing records it yet. Without a metric, operators still can't compare what a template's sandboxes use with what they are given. This PR has sandbox-manager's watchdog record each reading as the sandbox.resource.memory.guest_used_bytes distribution, tagged with the sandbox's template. It records only for probes it accepts (same lifecycle epoch, sandbox still tracked) of started sandboxes.

Example.

probe dispatched: sandbox S, template "seed", lifecycle started, epoch 4
guest replies memory_used_bytes = 307200000
result applied: epoch still 4, S still tracked -> guest_used_bytes{template:seed} = 3.072e8
same reply, but S paused (epoch 5) while the probe ran -> result discarded, nothing recorded
paused sandbox (a ready warm-pool slot) -> no Ping, nothing recorded

Verdict: comment, not approving yet. The gate is in the right place:

• the epoch fence and the started filter apply to the accepted result;
• the template comes from the cached row with no extra database read;
• health ignores the reading.

This head waits on #1668's rebase onto main and a green Pull CI run on the restacked head. Open #1624 changes the same probe scheduling, and #1703 touches watchdog.rs; whichever lands second rebases.

Before merge (inline threads)

1. The emitter's doc comment contradicts the docs and the code
2. The two new watchdog tests assert on telemetry population
3. PR description

Nits

• Metric name. sandbox.resource.memory.guest_used_bytes is the only sandbox.resource.* metric. It sits beside sandbox.guest.mem_total_bytes in the same module, with the same source and tag.
  • If you agree, rename it before merge, for example to sandbox.guest.mem_used_bytes; after merge, a rename moves dashboards to a new series.
  • A rename also changes docs/observability.md and #1670's Prometheus query.
• docs/observability.md:1245-1246: "about every 24 to 37 seconds". The delay is 24-36 s and dispatch rounds up to the 5 s scheduler tick, so "about every 25 to 40 seconds".

[ac-pplx]

The emitter's doc comment contradicts the docs and the code (crates/l40_api/sbx/mgr/server/src/metrics/sandbox/worker/guest_bridge.rs:52).

• It says the watchdog emits a sample "including idle warm-pool members".
• Ready slots are paused (docs/space/design/warm-pools.md:112), and probe_spaced_guest_health sends no Ping to a paused sandbox (watchdog.rs:2759). The second commit fixed docs/observability.md but not this comment.
• Suggested wording: "The watchdog emits one sample per accepted probe of a started sandbox; paused sandboxes, including ready warm-pool slots, are not pinged and record nothing."

[gilalon-pplx]

Fixed in 7801ea80d. The emitter documentation now matches the code: samples come from accepted probes of started sandboxes. Paused sandboxes, including ready warm-pool slots, are not pinged and record nothing; pool membership alone does not exclude a started sandbox.

_{Created with Perplexity}

[ac-pplx]

The two new watchdog tests assert on telemetry population (crates/l40_api/sbx/mgr/server/src/watchdog/tests.rs:1346, :1483).

• The repo's test rule (space-code-quality: "Do not write unit tests that assert on telemetry ... metric tags") excludes these.
• Several rows also don't test what they name:
  • apply_composed_health_result reads the database only for update_guest_uptime, so the pool_template rows repeat the paused and started rows;
  • the paused rows feed a reading that production never sends, because the probe returns none for a paused sandbox;
  • guest_memory_is_not_replayed_by_a_later_probe guards a cache that doesn't exist.
• Suggested fix: delete both tests. The existing lifecycle_edge_preserves_status_and_discards_in_flight_probe pins the epoch fence the reading rides on, and smoke: verify guest memory reaches local telemetry #1670's smoke covers delivery.
• Then drop the body's "cover both the paused unclaimed case and the running pool-marked case explicitly" and update the test count.

[gilalon-pplx]

Both telemetry-population tests remain removed in restacked head a3d33be05. The existing lifecycle_edge_preserves_status_and_discards_in_flight_probe test covers stale-probe rejection; the telemetry smoke owns backend delivery coverage. All 55 watchdog tests passed locally on the new combined stack, and the PR body no longer claims coverage from the removed acceptance table.

Fresh Pull CI at this head and the dependent #1670 delivery run are running. The smoke's multi-poll reset edge and stale generated index have been fixed in ded1ef354; local Python validation now includes the full CI runner, with its index gate and all 1,931 tests passing without skips.

_{Created with Perplexity}

[ac-pplx]

PR description.

• "Live Kind validation has not been rerun for this revision" isn't accurate. This PR's own Pull CI skipped Kind (watchdog.rs isn't in ci/kind-pull-paths.txt). But smoke: verify guest memory reaches local telemetry #1670's Pull CI ran local.telemetry_reaches_local_backends on Kind, with this PR's code, and received fresh samples. Cite that run, at the restacked head.
• "Update the observability documentation and the existing acceptance test table..." and "These changes correct the documented population and test cases" describe earlier revisions. CONTRIBUTING asks for what merging does.
• The repo squashes with COMMIT_MESSAGES and both commits are subject-only. Squash to one commit with an accurate message while rebasing.

[gilalon-pplx]

The description now matches restacked head a3d33be05, directly based on #1668's 5de789f85 and containing main 3a6e89f3b. The feature diff is unchanged: sandbox.guest.mem_used_bytes, template attribution, lifecycle fencing, paused ready-pool exclusion rather than a pool-membership filter, and approximately 25–40 second cadence.

Each PR is now one focused commit with a final-behavior message, removing obsolete intermediate subjects from this stack's squash-message input. Local validation on the new combined stack passed all 55 watchdog tests and strict Clippy.

Fresh Pull CI at this head is running. Delivery evidence will come from the dependent #1670 exact-head run; earlier-head CI is not being substituted for either result. The dependent smoke now retains effective baselines across detected resets and passes the generated-index check.

_{Created with Perplexity}

The pull request changed after this approval. CodeRabbit approves again after it reviews the current head.

[gilalon-pplx]

Addressed the metric-name and cadence suggestions in 7801ea80d. Renamed the metric to sandbox.guest.mem_used_bytes, alongside sandbox.guest.mem_total_bytes, and updated the observability documentation and the dependent smoke query.

The documented cadence is now approximately 25–40 seconds including scheduler rounding. The refreshed branch includes the guest-reporting merge, and the smoke branch includes this metric change.

_{Created with Perplexity}