fix(core): Inject replayId into trace context for buffer mode errors

[romtsn]

📜 Description

In buffer mode, the scope's replayId is intentionally empty until captureReplay() is called (to avoid tagging events with a replay that may never be sent). However, the event's DSC is built from the active transaction's frozen baggage, which was frozen before captureReplay() set the replayId. This means error events that trigger a buffer replay flush have no replay_id in their DSC, breaking error-to-replay linkage.

After captureReplay() runs, we now force-set the replayId on the transaction's frozen baggage via Baggage.forceSetReplayId(), so the envelope header carries the correct replay_id in the DSC. This mirrors the JS SDK's setReplayIdOnDynamicSamplingContext.

💡 Motivation and Context

Error events that trigger buffer-mode replay capture were not linked to the resulting replay, making it impossible to navigate from the error to its replay in the Sentry UI.

Example replay with a linked error event: https://sentry-sdks.sentry.io/explore/replays/49e737e2f6dc48f1a9c14692bd898bb7/?playlistEnd=2026-07-13T07:15:41&playlistStart=2026-07-06T07:15:41&project=5428559&query=&referrer=replayList&t_main=errors

💚 How did you test it?

• Existing SentryClientTest suite passes
• Manual verification with sample app in buffer mode: captured exception's DSC now contains the replay_id, and the error appears linked to the replay in Sentry

📝 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

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.48.0 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	327.25 ms	381.92 ms	54.67 ms
Size	0 B	0 B	0 B

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
6b019b7	319.84 ms	333.15 ms	13.31 ms
eb95ded	317.51 ms	369.08 ms	51.57 ms
319f256	317.53 ms	370.83 ms	53.29 ms
b3d8889	420.46 ms	453.71 ms	33.26 ms
6b019b7	403.90 ms	546.09 ms	142.19 ms
889ecea	367.58 ms	437.52 ms	69.94 ms
d15471f	303.49 ms	439.08 ms	135.59 ms
d364ace	384.53 ms	453.51 ms	68.98 ms
6ea4329	309.06 ms	353.48 ms	44.42 ms
c8125f3	383.82 ms	441.66 ms	57.84 ms

App size

Revision	Plain	With Sentry	Diff
6b019b7	0 B	0 B	0 B
eb95ded	0 B	0 B	0 B
319f256	1.58 MiB	2.19 MiB	619.79 KiB
b3d8889	1.58 MiB	2.10 MiB	535.07 KiB
6b019b7	0 B	0 B	0 B
889ecea	1.58 MiB	2.11 MiB	539.75 KiB
d15471f	1.58 MiB	2.13 MiB	559.54 KiB
d364ace	1.58 MiB	2.11 MiB	539.75 KiB
6ea4329	1.58 MiB	2.29 MiB	719.82 KiB
c8125f3	1.58 MiB	2.10 MiB	532.32 KiB

Previous results on branch: rz/fix/replay-error-linkage

Startup times

Revision	Plain	With Sentry	Diff
4f9605b	382.72 ms	476.24 ms	93.52 ms
9fbe087	391.26 ms	480.70 ms	89.44 ms
e6285ac	315.38 ms	353.88 ms	38.50 ms
cf20b6f	319.82 ms	356.96 ms	37.14 ms
01678a6	315.83 ms	347.92 ms	32.09 ms
7dd24bc	315.35 ms	363.57 ms	48.22 ms
48dcd0f	322.68 ms	374.14 ms	51.46 ms

App size

Revision	Plain	With Sentry	Diff
4f9605b	0 B	0 B	0 B
9fbe087	0 B	0 B	0 B
e6285ac	0 B	0 B	0 B
cf20b6f	0 B	0 B	0 B
01678a6	0 B	0 B	0 B
7dd24bc	0 B	0 B	0 B
48dcd0f	0 B	0 B	0 B

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