fix(core): [Unhandled Sessions 2] Make session cache writes session-id aware

[buenaflor]

PR Stack (Unhandled Sessions)

• feat(core): Unhandled Sessions #5915 (collection)
• feat(core): [Unhandled Sessions 1] Add Unhandled session state and non-terminating error flag #5919
• fix(core): [Unhandled Sessions 2] Make session cache writes session-id aware #5920
• feat(android): [Unhandled Sessions 3] Add internal non-terminating envelope capture #5921

---

📜 Description

Makes the session file cache aware of which session it is acting on.

Two paths in EnvelopeCache.storeInternal previously ignored session identity:

• SessionEnd deleted session.json unconditionally. A delayed End(A) arriving after a newer session B was persisted would delete B's file.
• SessionStart always rotated session.json into previous_session.json and overwrote it. A delayed Start(A) arriving after A's own state had already advanced on disk would overwrite the newer snapshot.

Both now compare session ids (and, for SessionEnd, start times) before deleting or rotating. A stale end only preserves the current file when the current session is genuinely newer — a different id and a later start time. Everything else keeps the existing behaviour, including malformed envelopes and unreadable session files, which still delete as before.

Also adds EnvelopeCache.persistCurrentSession(Session) so a caller can flush the active session to disk outside the envelope-store path, and extracts readSessionFromEnvelope / readSessionFromDisk helpers.

💡 Motivation and Context

Needed by the next PR in the stack, which mutates the live session in place (flagging a non-terminating unhandled error) and persists it so the flag survives process death. Without session-id awareness, an unrelated in-flight SessionEnd or SessionStart could clobber that snapshot.

In practice this only changes observable behaviour for sessions carrying the flag from PR 1 — the preserve branch requires hasNonTerminatingUnhandledError() — so existing SDK flows are unaffected.

💚 How did you test it?

EnvelopeCacheTest grew coverage for delayed same-id SessionStart preserving a newer unhandled or higher-error snapshot, different-id starts still rotating, matching and mismatching SessionEnd, null session ids on both paths, malformed envelopes, and unreadable session files. Also verified the pre-existing AbnormalExit and NativeCrashExit recovery paths still win over the flag. 36 tests, all passing.

📝 Checklist

• I added GH Issue ID & Linear ID
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

The capture API that sets the flag, in the next PR in this stack.

#skip-changelog

⚠️ Merge this PR using a merge commit (not squash). Only the collection branch is squash-merged into main.

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	343.87 ms	408.20 ms	64.33 ms
Size	0 B	0 B	0 B

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
6b019b7	343.31 ms	417.23 ms	73.91 ms
d15471f	286.65 ms	314.68 ms	28.03 ms
d217708	409.83 ms	474.72 ms	64.89 ms
d500866	326.13 ms	378.70 ms	52.58 ms
fcec2f2	314.96 ms	373.66 ms	58.70 ms
d501a7e	314.55 ms	343.34 ms	28.79 ms
7414e9b	322.49 ms	378.88 ms	56.39 ms
fcec2f2	357.47 ms	447.32 ms	89.85 ms
a416a65	316.52 ms	359.67 ms	43.15 ms
983e0f0	350.64 ms	386.44 ms	35.79 ms

App size

Revision	Plain	With Sentry	Diff
6b019b7	0 B	0 B	0 B
d15471f	1.58 MiB	2.13 MiB	559.54 KiB
d217708	1.58 MiB	2.10 MiB	532.97 KiB
d500866	0 B	0 B	0 B
fcec2f2	1.58 MiB	2.12 MiB	551.50 KiB
d501a7e	0 B	0 B	0 B
7414e9b	0 B	0 B	0 B
fcec2f2	1.58 MiB	2.12 MiB	551.50 KiB
a416a65	1.58 MiB	2.12 MiB	555.26 KiB
983e0f0	0 B	0 B	0 B

Previous results on branch: feat/unhandled-sessions-cache

Startup times

Revision	Plain	With Sentry	Diff
843e4f9	324.76 ms	399.16 ms	74.40 ms

App size

Revision	Plain	With Sentry	Diff
843e4f9	0 B	0 B	0 B

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.52.0 (1)	release

⚙️ sentry-android Build Distribution Settings