fix(core): Fix truncation to only keep last message in vercel

[nicohrubec]

• no longer set deprecated GEN_AI_PROMPT_ATTRIBUTE
• convertPromptToMessages did not handle inputs that were already in messages formats (fallback to []), which was seemingly the culprit for truncation failing
• set the original Vercel AI_PROMPT_ATTRIBUTE to the truncated messages format irrespective of the input as well, so that we get truncation for the original Vercel attribute as well (before we sent the all messages in the original namespace)

Tests:

• unit tests that convertPromptToMessages properly handles inputs that are already in messages format
• truncation tests for Vercel ai

Closes #19060

[github-actions]

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	25.33 kB	-	-
@sentry/browser - with treeshaking flags	23.83 kB	-	-
@sentry/browser (incl. Tracing)	42.14 kB	-	-
@sentry/browser (incl. Tracing, Profiling)	46.79 kB	-	-
@sentry/browser (incl. Tracing, Replay)	80.76 kB	-	-
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	70.41 kB	-	-
@sentry/browser (incl. Tracing, Replay with Canvas)	85.47 kB	-	-
@sentry/browser (incl. Tracing, Replay, Feedback)	97.66 kB	-	-
@sentry/browser (incl. Feedback)	42.05 kB	-	-
@sentry/browser (incl. sendFeedback)	30.02 kB	-	-
@sentry/browser (incl. FeedbackAsync)	35.01 kB	-	-
@sentry/browser (incl. Metrics)	26.43 kB	-	-
@sentry/browser (incl. Logs)	26.58 kB	-	-
@sentry/browser (incl. Metrics & Logs)	27.25 kB	-	-
@sentry/react	27.06 kB	-	-
@sentry/react (incl. Tracing)	44.38 kB	-	-
@sentry/vue	29.76 kB	-	-
@sentry/vue (incl. Tracing)	43.94 kB	-	-
@sentry/svelte	25.34 kB	-	-
CDN Bundle	27.9 kB	-	-
CDN Bundle (incl. Tracing)	42.93 kB	-	-
CDN Bundle (incl. Logs, Metrics)	28.74 kB	-	-
CDN Bundle (incl. Tracing, Logs, Metrics)	43.75 kB	-	-
CDN Bundle (incl. Replay, Logs, Metrics)	67.68 kB	-	-
CDN Bundle (incl. Tracing, Replay)	79.67 kB	-	-
CDN Bundle (incl. Tracing, Replay, Logs, Metrics)	80.54 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback)	85.12 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback, Logs, Metrics)	86.04 kB	-	-
CDN Bundle - uncompressed	81.61 kB	-	-
CDN Bundle (incl. Tracing) - uncompressed	127.16 kB	-	-
CDN Bundle (incl. Logs, Metrics) - uncompressed	84.45 kB	-	-
CDN Bundle (incl. Tracing, Logs, Metrics) - uncompressed	129.99 kB	-	-
CDN Bundle (incl. Replay, Logs, Metrics) - uncompressed	207.83 kB	-	-
CDN Bundle (incl. Tracing, Replay) - uncompressed	243.76 kB	-	-
CDN Bundle (incl. Tracing, Replay, Logs, Metrics) - uncompressed	246.58 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	256.56 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback, Logs, Metrics) - uncompressed	259.37 kB	-	-
@sentry/nextjs (client)	46.73 kB	-	-
@sentry/sveltekit (client)	42.51 kB	-	-
@sentry/node-core	52.08 kB	-0.01%	-2 B 🔽
@sentry/node	166.08 kB	+0.01%	+1 B 🔺
@sentry/node - without tracing	93.83 kB	-	-
@sentry/aws-serverless	109.36 kB	+0.01%	+1 B 🔺

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[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	8,626	-	8,725	-1%
GET With Sentry	1,658	19%	1,664	-0%
GET With Sentry (error only)	5,894	68%	6,107	-3%
POST Baseline	1,149	-	1,193	-4%
POST With Sentry	571	50%	597	-4%
POST With Sentry (error only)	1,022	89%	1,037	-1%
MYSQL Baseline	3,246	-	3,234	+0%
MYSQL With Sentry	435	13%	443	-2%
MYSQL With Sentry (error only)	2,612	80%	2,624	-0%

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